JastorffKG20093JJastorffZKourtziMAGiese2009-11-0044291402614038Journal of NeuroscienceRecognition of actions and complex movements is fundamental for social interactions and action understanding. While the relationship between motor expertise and visual recognition of body movements has received a vast amount of interest, the role of visual learning remains largely unexplored. Combining psychophysics and functional magnetic resonance imaging (fMRI) experiments, we investigated neural correlates of visual learning of complex movements. Subjects were trained to visually discriminate between very similar complex movement stimuli generated by motion morphing that were either compatible (experiments 1 and 2) or incompatible (experiment 3) with human movement execution. Employing an fMRI adaptation paradigm as index of discriminability, we scanned human subjects before and after discrimination training. The results of experiment 1 revealed three different effects as a consequence of training: (1) Emerging fMRI-selective adaptation in general motion-related areas (hMT/V5+, KO/V3b) for the differences between human-like movements. (2) Enhanced of fMRI-selective adaptation already present before training in biological motion-related areas (pSTS, FBA). (3) Changes covarying with task difficulty in frontal areas. Moreover, the observed activity changes were specific to the trained movement patterns (experiment 2). The results of experiment 3, testing artificial movement stimuli, were strikingly similar to the results obtained for human movements. General and biological motion-related areas showed movement-specific changes in fMRI-selective adaptation for the differences between the stimuli after training. These results support the existence of a powerful visual machinery for the learning of complex motion patterns that is independent of motor execution. We thus propose a key role of visual learning in action recognition.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published12Visual Learning Shapes the Processing of Complex Movement Stimuli in the Human Brain15017154221501715421WeigeltKSM20073SWeigeltZKourtziWSinglerLMuckli2007-04-00142738643874Journal of NeuroscienceThe perception of motion provides valuable interpolations of the visual scene. This fundamental capacity of the visual system is evident in apparent rotation: by presenting only two images of an object rotated in space, a vivid illusion of a smooth apparent motion in three dimensions can be induced. The unseen interpolated rotation views are filled in by the visual system. In the present study, we identified the cortical network responsible for this filling-in process. We argue that cross talk between areas of the ventral and dorsal visual pathways promote the illusion of smooth apparent rotation. Most interestingly, the network represents the unseen object views. Using functional magnetic resonance adaptation, we are able to show that the cortical network selectively adapts to the illusory object views. Our findings provide strong evidence for cortical representations of three-dimensional rotating objects that are view invariant with respect to the rotation path. Furthermore, our results confirm psychophysical investigations that unseen interpolated rotation views can be primed by apparent motion. By applying functional magnetic resonance adaptation, we show for the first time cortical adaptation to unseen objects. Together, our neuroimaging study advances the understanding of the cortical mechanisms mediating the influence of motion on object processing.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published10The Cortical Representation of Objects Rotating in Depth15017154221501715421ChandrasekaranCDKW20073CChandrasekaranVCanonJCDahmenZKourtziAEWelchman2007-02-0029715531565Journal of NeurophysiologyBinocular disparity, the slight differences between the images registered by our two eyes, provides an important cue when estimating the three-dimensional (3D) structure of the complex environment we inhabit. Sensitivity to binocular disparity is evident at multiple levels of the visual hierarchy in the primate brain, from early visual cortex to parietal and temporal areas. However, the relationship between activity in these areas and key perceptual functions that exploit disparity information for 3D shape perception remains an important open question. Here we investigate the link between human cortical activity and the perception of disparity-defined shape, measuring fMRI responses concurrently with psychophysical shape judgments. We parametrically degraded the coherence of shapes by shuffling the spatial position of dots whose disparity defined the 3D structure and investigated the effect of this stimulus manipulation on both cortical activity and shape discrimination. We report significant relationships between shape coherence and fMRI response in both dorsal (V3, hMT+/V5) and ventral (LOC) visual areas that correspond to the observers' discrimination performance. In contrast to previous suggestions of a dichotomy of disparity-related processes in the ventral and dorsal streams, these findings are consistent with proposed interactions between these pathways that may mediate a continuum of processes important in perceiving 3D shape from coarse contour segmentation to fine curvature estimation.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published12Neural Correlates of Disparity-Defined Shape Discrimination in the Human Brain1501715422TjanLK20063BSTjanVLestouZKourtzi2006-09-0039615561568Journal of NeurophysiologyThe way in which input noise perturbs the behavior of a system depends on the internal processing structure of the system. In visual psychophysics, there is a long tradition of using external noise methods (i.e., adding noise to visual stimuli) as tools for system identification. Here, we demonstrate that external noise affects processing of visual scenes at different cortical areas along the human ventral visual pathway, from retinotopic regions to higher occipitotemporal areas implicated in visual shape processing. We found that when the contrast of the stimulus was held constant, the further away from the retinal input a cortical area was the more its activity, as measured with functional magnetic resonance imaging (fMRI), depended on the signal-to-noise ratio (SNR) of the visual stimulus. A similar pattern of results was observed when trials with correct and incorrect responses were analyzed separately. We interpret these findings by extending signal detection theory to fMRI data analysis. This approach reveals the sequential ordering of decision stages in the cortex by exploiting the relation between fMRI response and stimulus SNR. In particular, our findings provide novel evidence that occipitotemporal areas in the ventral visual pathway form a cascade of decision stages with increasing degree of signal uncertainty and feature invariance.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published12Uncertainty and Invariance in the Human Visual Cortex1501715422JastorffKG20063JJastorffZKourtziMAGiese2006-07-0086791804Journal of VisionThe recognition of complex body movements and actions is a fundamental visual capacity very important for social communication. It seems possible that movement recognition is based on a general capability of the visual system to learn complex visual motion patterns. Alternatively, this visual function might exploit specialized mechanisms for the analysis of biologically relevant movements, for example, of humans or animals. To investigate this question, we trained human observers to discriminate novel motion patterns that were generated, exploiting a new technique for stimulus generation by motion morphing. We tested the learning of different classes of novel movement stimuli. One group of stimuli was fully consistent with human movements. A second class of stimuli was based on artificial skeleton models that were inconsistent with human and animal bodies. A third group of stimuli specified the same local motion information as human movements but was inconsistent with an underlying articulated shape. Participants learned both classes of articulated movements very fast in an orientation-dependent manner. Learning speed and accuracy were strikingly similar and independent of the similarity of the stimuli with biologically relevant body shapes. For the class of stimuli without underlying articulated shape, however, we did not observe significant improvements of the discrimination performance after training. Our results indicate the existence of a fast visual learning process for complex articulated movement patterns, which likely is relevant for biological motion perception. This process seems to operate independently of the consistency of the patterns with biologically relevant body shapes but seems to require the compatibility of the learned movements with a global underlying shape.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published13Learning to discriminate complex movements: Biological versus artificial trajectories1501715422150171542139873ZKourtziMAugathNKLogothetisAMovshonLKiorpes2006-03-00424359366Magnetic Resonance ImagingWe studied the development of visual activation longitudinally in two infant monkeys aged 103561 days using the BOLD fMRI technique under opiate anesthesia and compared the results with those obtained in three adult animals studied under identical conditions. Visual activation in primary visual cortex, V1, was strong and reliable in monkeys of the youngest and oldest ages, showing that functional imaging techniques give qualitatively similar results in infants and adults. Visual activation in extrastriate areas involved in processing motion (MT/V5) and form (V4) was not evident in the younger animals, but became more adult-like in the older animals. This delayed onset of measurable BOLD responses in extrastriate visual cortex may reflect delayed development of visual responses in these areas, although at this stage it is not possible to rule out either effects of anesthesia or of changes in cerebral vascular response mechanisms as the cause. The demonstration of visually evoked BOLD responses in young monkeys shows that the BOLD fMRI technique can usefully be employed to address functional questions of brain development.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published7Development of visually evoked cortical activity in infant macaque monkeys studied longitudinally with fMRI1501715421KrekelbergVK20053BKrekelbergAVatakisZKourtzi2005-12-0069443734386Journal of NeurophysiologyWhen cartoonists use speed lines—also called motion streaks—to suggest the speed of a stationary object, they use form to imply motion. The goal of this study was to investigate the mechanisms that mediate the percept of implied motion in the human visual cortex. In an adaptation functional imaging paradigm we presented Glass patterns that, just like speed lines, imply motion but do not on average contain coherent motion energy. We found selective adaptation to these patterns in the human motion complex, the lateral occipital complex (LOC), and earlier visual areas. Glass patterns contain both local orientation features and global structure. To disentangle these aspects we performed a control experiment using Glass patterns with minimal local orientation differences but large global structure differences. This experiment showed that selectivity for Glass patterns arises in part in areas beyond V1 and V2. Interestingly, the selective adaptation transferred from implied motion stimuli to similar real motion patterns in dorsal but not ventral areas. This suggests that the same subpopulations of cells in dorsal areas that are selective for implied motion are also selective for real motion. In other words, these cells are invariant with respect to the cue (implied or real) that generates the motion. We conclude that the human motion complex responds to Glass patterns as if they contain coherent motion. This, presumably, is the reason why these patterns appear to move coherently. The LOC, however, has different cells that respond to the structure of real motion patterns versus implied motion patterns. Such a differential response may allow ventral areas to further analyze the structure of global patterns.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published13Implied Motion From Form in the Human Visual Cortex1501715421150171542234873ZKourtziEHuberle2005-11-00228440452NeuroImageThe integration of local elements to coherent forms is at the core of understanding visual perception. Accumulating evidence suggests that both early retinotopic and higher occipitotemporal areas contribute to the integration of local elements to global forms. However, the spatiotemporal characteristics of form analysis in the human visual cortex remain largely unknown. The aim of this study was to investigate form analysis at different spatial (global vs. local structure) and temporal (different stimulus presentation rates) scales across stages of visual analysis (from V1 to the lateral occipital complex—LOC) in the human brain. We used closed contours rendered by Gabor elements and manipulated either the global contour structure or the orientation of the local Gabor elements. Our rapid event-related fMRI adaptation studies suggest that contour integration and form processing in early visual areas is transient and limited within the local neighborhood of their cells' receptive field. In contrast, higher visual areas appear to process the perceived global form in a more sustained manner. Finally, we demonstrate that these spatiotemporal properties of form processing in the visual cortex are modulated by attention. Attention to the global form maintains sustained processing in occipitotemporal areas, whereas attention to local elements enhances their integration in early visual areas. These findings provide novel neuroimaging evidence for form analysis at different spatiotemporal scales across human visual areas and validate the use of rapid event-related fMRI adaptation for investigating processing across stages of visual analysis in the human brain.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published12Spatiotemporal characteristics of form analysis in the human visual cortex revealed by rapid event-related fMRI adaptation1501715422150171542133263KMoutoussisGAKelirisZKourtziNKLogothetis2005-08-0017452231–2243Vision ResearchThe relationship between brain activity and conscious visual experience is central to our understanding of the neural mechanisms underlying perception. Binocularrivalry, where monocular stimuli compete for perceptual dominance, has been previously used to dissociate the constant stimulus from the varying percept. We report here fMRI results from humans experiencing binocularrivalry under a dichoptic stimulation paradigm that consisted of two drifting random dot patterns with different motion coherence. Each pattern had also a different color, which both enhanced rivalry and was used for reporting which of the two patterns was visible at each time. As the perception of the subjects alternated between coherent motion and motion noise, we examined the effect that these alternations had on the strength of the MR signal throughout the brain. Our results demonstrate that motionperception is able to modulate the activity of several of the visual areas which are known to be involved in motion processing. More specifically, in addition to area V5 which showed the strongest modulation, a higher activity during the perception of motion than during the perception of noise was also clearly observed in areas V3A and LOC, and less so in area V3. In previous studies, these areas had been selectively activated by motion stimuli but whether their activity reflects motionperception or not remained unclear; here we show that they are involved in motionperception as well. The present findings therefore suggest a lack of a clear distinction between ‘processing’ versus ‘perceptual’ areas in the brain, but rather that the areas involved in the processing of a specific visual attribute are also part of the neuronal network that is collectively responsible for its perceptual representation.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-2231A binocular rivalry study of motion perception in the human brain150171542133003CAltmannWGroddZKourtziHHBülthoffH-OKarnath2005-08-00144321012108NeuropsychologiaVisual object perception has been suggested to follow two different routes in the human brain: a ventral, view-invariant occipitaltemporal route processes object identity, whereas a dorsal, view-dependent occipitalparietal route processes spatial properties of an object. Using fMRI, we addressed the question whether these routes are exclusively involved in either object recognition or spatial representation. We presented subjects with images of natural objects and involved them either in object identification or object orientation judgment task. For both tasks, we observed activation in ventro-temporal as well as parietal areas bilaterally, with significantly stronger responses for the orientation judgment in both ventro-temporal as well as parietal areas. Our findings suggest that object identification and orientation judgment do not follow strictly separable cortical pathways, but rather involve both the dorsal and the ventral stream.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de//fileadmin/user_upload/files/publications/Altmann-etal-Neuropsychologia-2005_3300[0].pdfpublished7Similar cortical correlates underlie visual object identification and orientation judgment150171542234743ZKourtziLRBettsPSarkheilAEWelchman2005-06-007313171327PLoS BiologyExpertise in recognizing objects in cluttered scenes is a critical skill for our interactions in complex environments and is thought to develop with learning. However, the neural implementation of object learning across stages of visual analysis in the human brain remains largely unknown. Using combined psychophysics and functional magnetic resonance imaging (fMRI), we show a link between shape-specific learning in cluttered scenes and distributed neuronal plasticity in the human visual cortex. We report stronger fMRI responses for trained than untrained shapes across early and higher visual areas when observers learned to detect low-salience shapes in noisy backgrounds. However, training with high-salience pop-out targets resulted in lower fMRI responses for trained than untrained shapes in higher occipitotemporal areas. These findings suggest that learning of camouflaged shapes is mediated by increasing neural sensitivity across visual areas to bolster target segmentation and feature integration. In contrast, learning of prominent pop-out shapes is mediated by associations at higher occipitotemporal areas that support sparser coding of the critical features for target recognition. We propose that the human brain learns novel objects in complex scenes by reorganizing shape processing across visual areas, while taking advantage of natural image correlations that determine the distinctiveness of target shapes.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de//fileadmin/user_upload/files/publications/pdf3474.pdfpublished10Distributed Neural Plasticity for Shape Learning in the Human Visual Cortex1501715422150171542134383AEWelchmanADeubeliusVConradHHBülthoffZKourtzi2005-05-0068820827Nature NeuroscienceOur perception of the world&lsquo;s three-dimensional (3D) structure is critical for object recognition, navigation and planning actions. To accomplish this, the brain combines different types of visual information about depth structure, but at present, the neural architecture mediating this combination remains largely unknown. Here, we report neuroimaging correlates of human 3D shape perception from the combination of two depth cues. We measured fMRI responses while observers judged the 3D structure of two sequentially presented images of slanted planes defined by binocular disparity and perspective. We compared the behavioral and fMRI responses evoked by changes in one or both of the depth cues. fMRI responses in extrastriate areas (hMT+/V5 and lateral occipital complex), rather than responses in early retinotopic areas, reflected differences in perceived 3D shape, suggesting &lsquo;combined-cue&lsquo; representations in higher visual areas. These findings provide insight into the neural circuits engaged when the human brain combines different information sources for unified 3D visual perception.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de//fileadmin/user_upload/files/publications/pdf3438.pdfpublished73D shape perception from combined depth cues in human visual cortex150171542224153CFAltmannADeubeliusZKourtzi2004-06-00516794804Journal of Cognitive NeuroscienceVisual context influences our perception of target objects in natural scenes. However, little is known about the analysis of context information and its role in shape perception in the human brain. We investigated whether the human lateral occipital complex (LOC), known to be involved in the visual analysis of shapes, also processes information about the context of shapes within cluttered scenes. We employed an fMRI adaptation paradigm in which fMRI responses are lower for two identical than for two different stimuli presented consecutively. The stimuli consisted of closed target contours defined by aligned Gabor elements embedded in a background of randomly oriented Gabors. We measured fMRI adaptation in the LOC across changes in the context of the target shapes by manipulating the position and orientation of the background elements. No adaptation was observed across context changes when the background elements were presented in the same plane as the target elements. However, adaptation was observed when the grouping of the target elements was enhanced in a bottom-up (i.e., grouping by disparity or motion) or top-down (i.e., shape priming) manner and thus the saliency of the target shape increased. These findings suggest that the LOC processes information not only about shapes, but also about their context. This processing of context information in the LOC is modulated by figureground segmentation and grouping processes. That is, neural populations in the LOC encode context information when relevant to the perception of target shapes, but represent salient targets independent of context changes.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published10Shape saliency modulates contextual processing in the human Lateral Occipital Complex150171542233313ZKourtzi2004-02-00284749Trends in Cognitive SciencesA striking example of our sensitivity to dynamic information is our ability to infer motion from still images depicted in paintings, photographs or cartoons. What are the neural mechanisms that mediate this implied motion perception? In a recent paper, Krekelberg et al. demonstrate that form cues that imply motion are integrated with real motion information, and influence perception in both humans and monkeys and the neural processing in prototypical motion areas of the monkey brain.
Perception and successful interaction with moving objects entail that the visual system integrates information from form and motion cues into unified dynamic perceptual events. However, traditionally, shape and motion processing have been attributed to anatomically and functionally separable neural pathways in the primate brain [1]. An extrastriate visual area in the medial temporal monkey brain (MT/V5) and its human analogue in the ascending limb of the inferior temporal sulcus (hMT+/V5) have been identified as one of the main regions involved in the analysis of visual motion [2] and [3]. By contrast, regions in the occipitotemporal cortex (V4, IT) have been implicated in the analysis of shape properties and object recognition in the monkey and the human brain [4] and [5].
Although significant progress has been made in uncovering the neural mechanisms that mediate motion and form perception, surprisingly little is known about possible interactions of these mechanisms that may underlie the unified perception of moving objects in our dynamic visual environments. Krekelberg et al.[6] provide evidence for such interactions by showing similar responses in monkey MT and MST cells to real motion and static form patterns that have no coherent physical motion but imply motion. These physiological findings are consistent with the perception of their human and monkey subjects.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published2"But still, it moves"1501715421KourtziEGB20033ZKourtziMErbWGroddHHBülthoff2003-09-00913911920Cerebral CortexWe used human functional magnetic resonance imaging (fMRI) to test whether the human lateral occipital complex (LOC), an area known to be involved in the analysis of visual shape, represents the perceived 3-D shape of objects or simply their 2-D contours. We employed an fMRI adaptation paradigm, in which repeated presentation of a stimulus results in decreased responses compared to responses to different stimuli. We found adaptation in the LOC for images of objects with the same perceived 3-D shape structure but different 2-D contours that resulted from small rotations of the objects in the frontal plane or in depth. However, no adaptation was observed in the LOC for images of objects that had the same 2-D contours but differed in their perceived 3-D shape; namely, 2-D silhouettes versus 3-D shaded images of objects, or convex versus concave objects. Differences in the fMRI adaptation responses across subregions in the LOC suggest that different neural populations in the LOC may mediate different mechanisms for the processing of object features.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published9Representation of the perceived 3-D object shape in the human lateral occipital complex150171542220133CFAltmannHHBülthoffZKourtzi2003-02-00413342349Current BiologyThe question of how local image features on the retina are integrated into perceived global shapes is central to our understanding of human visual perception. Psychophysical investigations have suggested that the emergence of a coherent visual percept, or a "good-Gestalt", is mediated by the perceptual organization of local features based on their similarity. However, the neural mechanisms that mediate unified shape perception in the human brain remain largely unknown. Using human fMRI, we demonstrate that not only higher occipitotemporal but also early retinotopic areas are involved in the perceptual organization and detection of global shapes. Specifically, these areas showed stronger fMRI responses to global contours consisting of collinear elements than to patterns of randomly oriented local elements. More importantly, decreased detection performance and fMRI activations were observed when misalignment of the contour elements disturbed the perceptual coherence of the contours. However, grouping of the misaligned contour elements by disparity resulted in increased performance and fMRI activations, suggesting that similar neural mechanisms may underlie grouping of local elements to global shapes by different visual features (orientation or disparity). Thus, these findings provide novel evidence for the role of both early feature integration processes and higher stages of visual analysis in coherent visual perception.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de//fileadmin/user_upload/files/publications/pdf2013.pdfpublished7Perceptual organization of local elements into global shapes in the human visual cortex150171542220673ZKourtziASToliasCFAltmannMAugathNKLogothetis2003-01-00237333346NeuronThe integration of local image features into global shapes was investigated in monkeys and humans using fMRI. An adaptation paradigm was used, in which stimulus selectivity was deduced by changes in the course of adaptation of a pattern of randomly oriented elements. Accordingly, we observed stronger activity when orientation changes in the adapting stimulus resulted in a collinear contour than a different random pattern. This selectivity to collinear contours was observed not only in higher visual areas that are implicated in shape processing, but also in early visual areas where selectivity depended on the receptive field size. These findings suggest that unified shape perception in both monkeys and humans involves multiple visual areas that may integrate local elements to global shapes at different spatial scales.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de//fileadmin/user_upload/files/publications/pdf2067.pdfpublished13Integration of Local Features into Global Shapes: Monkey and Human fMRI Studies1501715422150171542113613IMThorntonZKourtzi2002-01-00131113132PerceptionIn a series of three experiments, we used a sequential matching task to explore the impact of non-rigid facial motion on the perception of human faces. Dynamic prime images, in the form of short video sequences, facilitated matching responses relative to a single static prime image. This advantage was observed whenever the prime and target showed the same face but an identity match was required across expression (experiment 1) or view (experiment 2). No facilitation was observed for identical dynamic prime sequences when the matching dimension was shifted from identity to expression (experiment 3). We suggest that the observed dynamic advantage, the first reported for non-degraded facial images, arises because the matching task places more emphasis on visual working memory than typical face recognition tasks. More specifically, we believe that representational mechanisms optimised for the processing of motion and/or change-over-time are established and maintained in working memory and that such 'dynamic representations' (Freyd, 1987 Psychological Review 94 427 - 438) capitalise on the increased information content of the dynamic primes to enhance performance.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de//fileadmin/user_upload/files/publications/pdf1361.pdfpublished19A matching advantage for dynamic human faces15017154226443ZKourtziHHBülthoffMErbWGrodd2002-01-00151718Nature NeuroscienceThe perception of moving objects and our successful interaction with them entail that the visual system integrates shape and motion information about objects. However, neuroimaging studies have implicated different human brain regions in the analysis of visual motion1, 2 (medial temporal cortex; MT/MST) and shape3, 4 (lateral occipital complex; LOC), consistent with traditional approaches in visual processing that attribute shape and motion processing to anatomically and functionally separable neural mechanisms. Here we demonstrate object-selective fMRI responses (higher responses for intact than for scrambled images of objects) in MT/MST, and especially in a ventral subregion of MT/MST, suggesting that human brain regions involved mainly in the processing of visual motion are also engaged in the analysis of object shape.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de//fileadmin/user_upload/files/publications/pdf644.pdfpublished1Object-selective responses in the human motion area MT/MST1501715422413ZKourtziNKanwisher2001-08-00553429315061509ScienceThe human lateral occipital complex (LOC) has been implicated in object recognition, but it is unknown whether this region represents low-level image features or perceived object shape. We used an event-related functional magnetic resonance imaging adaptation paradigm in which the response to pairs of successively presented stimuli is lower when they are identical than when they are different. Adaptation across a change between the two stimuli in a pair provides evidence for a common neural representation invariant to that change. We found adaptation in the LOC when perceived shape was identical but contours differed, but not when contours were identical but perceived shape differed. These data indicate that the LOC represents not simple image features, but rather higher level shape information.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de//fileadmin/user_upload/files/publications/pdf41.pdfpublished3Representation of perceived object shapes by the human lateral occipital complex.150171542213553ZKourtziKNakayama2001-04-001-29248264Visual CognitionThe visual system has been suggested to integrate different views of an object in motion. We investigated differences in the way moving and static objects are represented by testing for priming effects to previously seen ("known") and novel object views. We showed priming effects for moving objects across image changes (e.g. mirror reversals, changes in size, and changes in polarity) but not over temporal delays. The opposite pattern of results was observed for objects presented statically; that is, static objects were primed over temporal delays but not across image changes. These results suggest that representations for moving objects (1) are updated continuously across image changes while static object representations generalize only across similar images and (2) they are more short-lived than static object representations. These results suggest two distinct representational mechanisms; a static object mechanism rather spatially refined and permanent, possibly suited for visual recognition and a motion-based object mechanism more temporary and less spatially refined, possibly suited for visual guidance of motor actions.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de//fileadmin/user_upload/files/publications/pdf1355.pdfpublished16Distinct mechanisms for the representation of moving and static objects1501715422423ZKourtziMShiffrar2001-04-00227335355Journal of Experimental Psychology: Human Perception and PerformanceMost studies and theories of object recognition have addressed the perception of rigid objects. Yet, physical objects may also move in a nonrigid manner. A series of priming studies examined the conditions under which observers can recognize novel views of objects moving nonrigidly. Observers were primed with 2 views of a rotating object that were linked by apparent motion or presented statically. The apparent malleability of the rotating prime object varied such that the object appeared to be either malleable or rigid. Novel deformed views of malleable objects were primed when falling within the object's motion path. Priming patterns were significantly more restricted for deformed views of rigid objects. These results suggest that moving malleable objects may be represented as continuous events, whereas rigid objects may not. That is, object representations may be "dynamically remapped" during the analysis.of the object's motion.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published20Visual representation of malleable and rigid objects that deform as they rotate150171542218173ZKourtziNKanwisher2000-05-0092033103318Journal of NeuroscienceThe studies described here use functional magnetic resonance imaging to test whether common or distinct cognitive and/or neural mechanisms are involved in extracting object structure from the different image cues defining an object's shape, such as contours, shading, and monocular depth cues. We found overlapping activations in the lateral and ventral occipital cortex [known as the lateral occipital complex (LOC)] for objects defined by different visual cues (e.g., grayscale photographs and line drawings) when each was compared with its own scrambled-object control. In a second experiment we found a reduced response when objects were repeated, independent of whether they appeared in the same or a different format (i.e., grayscale images vs line drawings). A third experiment showed that activation in the LOC was no stronger for three-dimensional shapes defined by contours or monocular depth cues, such as occlusion, than for two-dimensional shapes, suggesting that these regions are not selectively involved in processing three-dimensional shape information. These results suggest that common regions in the LOC are involved in extracting and/or representing information about object structure from different image cues.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de//fileadmin/user_upload/files/publications/pdf1817.pdfpublished8Cortical Regions Involved in Perceiving Object Shape150171542218183ZKourtziNKanwisher2000-01-001124855Journal of cognitive neuroscienceA still photograph of an object in motion may convey dynamic information about the position of the object immediately before and after the photograph was taken (implied motion). Medial temporal/medial superior temporal cortex (MT/MST) is one of the main brain regions engaged in the perceptual analysis of visual motion. In two experiments we examined whether MT/MST is also involved in representing implied motion from static images. We found stronger functional magnetic resonance imaging (fMRI) activation within MT/MST during viewing of static photographs with implied motion compared to viewing of photographs without implied motion. These results suggest that brain regions involved in the visual analysis of motion are also engaged in processing implied dynamic information from static images.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de//fileadmin/user_upload/files/publications/pdf1818.pdfpublished7Activation in Human MT/MST by Static Images with Implied MotionKourtziG20052ZKourtziKGrill-SpectorOxford University PressOxford, UK2005-00-00173188Fitting the Mind to the World: Adaptation and After-Effects in High-Level VisionThis chapter describes how adaptation over short time frames (seconds) can be combined with brain imaging to study visual representations in the primate brain. The fMRI-adaptation approach, developed by Grill-Spector and her colleagues, exploits the fact that the fMRI response is reduced by repeated presentation of the same stimulus, which they attribute to the suppression of stimulus-specific neurons. Therefore, if a change in a stimulus dimension causes an increased response or ‘rebound’ from adaptation, then the population of neurons must be selective for, or code, that property. If adaptation remains constant across a change, then the population coding must be invariant to that property.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published15fMRI Adaptation: A Tool for Studying Visual Representations in the Primate Brain1501715422150171542144992ASToliasZKourtziNKLogothetisMIT PressCambridge, MA, USA2003-00-00109125Exploratory analysis and data modeling in functional neuroimagingFunctional magnetic resonance imaging can be used to study the networks of neurons that underline different behaviors. The blood oxygenation level-dependent signal though, measures the activity averaged across heterogeneous population of neurons with different response characteristics. It is therefore often impossible to infer the properties of the underlying imaged neural populations by simply examining the fMRI signal. Here, we describe the use of an adaptation paradigm to study the properties of neuronal populations beyond the spatial resolution of fMRI.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published16Functional magnetic resonance imaging adaptation: a technique for studying the properties of neuronal networks1501715421vanGrootelMMKMLK20127TJvan GrootelAMeesonMHJMunkZKourtziJAMovshonNKLogothetisLKiorpesNew Orleans, LA, USA2012-10-1542nd Annual Meeting of the Society for Neuroscience (Neuroscience 2012)In typical adult visual processing, low-level visual features are integrated into a global construct that enables the recognition of an object. Behaviorally, young primates are impaired at integrating global form and motion cues. Also the neural machinery to support global processing is not fully developed. However, earlier studies using single-unit electrophysiology show that neuronal response properties are relatively mature compared to behavioral capability. Behavioral sensitivity to global stimuli continues to improve for months or years beyond the time that neuronal responses are adult-like. To understand this discrepancy, we used a larger scale method to investigate cortical development, functional MRI.
We tracked the development of BOLD activation in striate and extra-striate cortex of macaque monkeys (Macaca mulatta) longitudinally over 2-3 years. The animals were imaged at 4.7T while anesthetized and paralyzed. To segregate dorsal and ventral stream activity, we used stationary and dynamic Glass pattern stimuli. These have comparable local features (dipoles) but different global forms (concentric or radial) and responses were compared to random-dipole patterns having the same overall statistics. We analyzed responses to a variety of spatial and spatio-temporal stimuli using multi-voxel pattern analysis (MVPA). We determined how classification accuracy depended on the cumulative number of voxels from different cortical areas using a support vector machine (SVM). In young monkeys (age < 2 years), we observed high classification accuracies in primary visual cortex (V1) when Glass patterns were present or absent (stimulus vs. blank) but lower accuracy for static vs. dynamic patterns. Only 2/10 imaging sessions yielded accuracies significantly higher than chance for the same contrast in extrastriate area MT of young monkeys. These same comparisons consistently produced high classification accuracy in animals older than 2 years. These results indicate that BOLD signal differences can be measured at young ages with a Glass pattern stimulus. However, signals related to pattern type are not distinguished reliably until older ages. These results complement our earlier findings showing late onset of activation patterns in extrastriate cortex (Kourtzi et al., 2006, Mag Res Imaging).nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published0Longitudinal fMRI study of cortical development in young monkeys150171542148277VCoradZKourtziAWelchmanTübingen, Germany2006-03-00509th Tübingen Perception Conference (TWK 2006)Ambiguous figure reversal involves a neural mechanism that limits the number of perceptual
organizations that can be consciously experienced at a given moment. So how can perceptual
experience be stable and continuous in the presence of alternative interpretations of the same
physical stimulus? Recent demonstrations using bistable stimuli such as the Necker cube have
revealed that repetitive intermittent presentation leads to a stabilization of the percept [1,2].
According to Gepshtein and Kubovy [3] two temporal processes play an important role in the
perception of ambiguous figures: adaptation and hysteresis. In the present study we investigated
the effects of reference stimulus duration and interstimulus interval length upon transition
probability using ambiguous and unambiguous versions of the Mach Card. On the basis of previous
research findings we predicted that long preexposure periods to the reference stimulus
lead to adaptation effects. Furthermore we hypothesized that the length of the interstimulus interval
between reference and test stimulus affects the subsequent perception of the ambiguous
test stimulus. As expected, participants displayed a convex bias in their responses to the ambiguous
Mach Card reference stimulus—indicating that they perceived the ambiguous Mach
Card as a standing book with the spine pointing towards them. The results of the present experiment
suggest that prolonged duration times of ambiguous and unambiguous reference stimuli
lead to adaptation effects in the perception of the ambiguous test stimulus. Examining the effects
of different interstimulus interval lengths, we demonstrated that short reference stimulus
duration times in combination with long interstimulus intervals seem to lock the percept in
its present state and the subsequent ambiguous test stimulus will be perceived in the identical
configuration. Further analysis will reveal if different adaptation and priming mechanisms are
active for convex and concave images, given the inherent tuning of the visual system to convexity.
The investigation of these history effects will help us to identify the relative contribution of
stimulus-driven and cognitive factors to the perception of ambiguous 3D shapes.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-50Breaking the Stability of Perceptual Instability: Adaptation and Priming in Ambiguous Figure Perception150171542232497PSarkheilJJastorffMGieseZKourtziSarasota, FL, USA2005-09-00847Fifth Annual Meeting of the Vision Sciences Society (VSS 2005)The ability to categorize actions is critical for
interacting in complex environments. Previous studies have
examined the neural correlates of categorization using
static stimuli. The goal of our study was to investigate
the neural substrates that mediate learning of complex
movement categories in the human brain. We used novel
dynamic patterns that were generated by animation of an
artificial skeleton model and presented as point-light
displays. We created prototypical stimuli that differed in
the spatial arrangement of their segments and their
kinematics. Intermediate stimuli between the prototypes
were generated by a weighted linear combination of the
prototypical trajectories in space-time. We compared fMRI
activations when the observers performed a categorization
vs. a spatial discrimination task on the same stimuli. In
the categorization task, the observers discriminated
whether each stimulus belonged to one of four prototypical
classes. In the spatial discrimination task, the observers
judged whether each stimulus was rotated (or translated)
leftwards vs. rightwards. These tasks were matched for
difficulty based on the observers? Performance during a
practice session. We observed significantly stronger fMRI
activations for the categorization than the spatial
discrimination tasks in the dorsal, inferior parietal and
the medial, inferior frontal cortex, consistent with
previous findings on the categorization of static stimuli.
Interestingly, we also observed activations in visual motion
areas (V3a, hMT+/V5), higher-order motion areas in the
intraparietal sulcus (VOIPS, POIPS, DIPSM, DIPSA) and
parieto-frontal areas (supramarginal gyrus, postcentral
gyrus, ventral and dorsal premotor cortex) thought to be
involved in action observation and imitation. These
findings suggest that categorization of complex dynamic
patterns may modulate processing in areas implicated in the
analysis of visual motion and actions.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-847Categorization of complex dynamic patterns in the human brain15017154221501715421ZvyagintsevMSVKM20057MZvyagintsevHMenningKSwirszczAVatakisZKourtziKMathiakTübingen, Germany2005-02-001918th Tübingen Perception Conference (TWK 2005)Apparent motion is the perception of the realistic smooth motion of an object which flashes or sounds first at one place and then at another. In a whole-head magnetoencephalography study, we assessed neural correlates of multisensory perception of apparent motion in 12 healthy
volunteers. Two successive disks (1 diameter, 100 cm distance, ±6 eccentricity, 67 ms duration, 67 ms ISI) were displayed simultaneously with auditory white noise signals (simulated by means of auditory virtual reality at the same locations). Conditions with self-induced and random direction were compared. During the first condition, the direction of apparent motion stimuli was determined by the button press of the subject and during the second, the stimulus direction was selected randomly. The time of stimulus onset was self-induced in both conditions.
Subjects were instructed to determine direction of motion after every sweep. We recorded 4 sessions with 260 sweeps in each subject. Similar evoked response fields were observed for self-induced and randomized sequences up to 140 ms after stimulus onset. The pattern accorded to distributed neuromagnetic activity. Peaking at about 160 ms, the difference field between the predictable and un-predictable condition exhibited a bilateral dipolar field structure with a higher negativity for the unpredictable stimulus directions. This pattern accords to
the N1 component of auditory evoked fields. Globally, apparent motion seems to engage areas related to auditory, visual, and motor processing and posterior parietal regions. As the main contrast of interest of our study, predictable versus un-predictable, i.e., self-induced vs. random, directions affected in first place auditory areas. In a similar vein, stimulus adaptation in the auditory domain has been observed during the perception of one’s own speech. This specific mechanism seems to be of high neurobiological importance as impairments of these—mainly
auditory—anticipatory projections have been suggested to be influential for hallucinations in schizophrenia.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-191Audio-Visual Perception of Self-Induced Apparent Motion150171542232477PSarkheilJJastorffMAGieseZKourtziTübingen, Germany2005-02-001888th Tübingen Perception Conference (TWK 2005)The ability to categorize actions is critical for
interacting in complex environments. Previous studies have
examined the neural correlates of categorization using
static stimuli. The goal of our study was to investigate
the neural substrates that mediate learning of complex
movement categories in the human brain. We used novel
dynamic patterns that were generated by animation of an
artificial skeleton model and presented as point-light
displays. We created prototypical stimuli that differed in
the spatial arrangement of their segments and their
kinematics. Intermediate stimuli between the prototypes
were generated by a weighted linear combination of the
prototypical trajectories in space-time. We compared fMRI
activations when the observers performed a categorization
vs. a spatial discrimination task on the same stimuli. In
the categorization task, the observers discriminated
whether each stimulus belonged to one of four prototypical
classes. In the spatial discrimination task, the observers
judged whether each stimulus was rotated (or translated)
leftwards vs. rightwards. These tasks were matched for
difficulty based on the observers? Performance during a
practice session. We observed significantly stronger fMRI
activations for the categorization than the spatial
discrimination tasks in the dorsal, inferior parietal and
the medial, inferior frontal cortex, consistent with
previous findings on the categorization of static stimuli.
Interestingly, we also observed activations in visual motion
areas (V3a, hMT+/V5), higher-order motion areas in the
intraparietal sulcus (VOIPS, POIPS, DIPSM, DIPSA) and
parieto-frontal areas (supramarginal gyrus, postcentral
gyrus, ventral and dorsal premotor cortex) thought to be
involved in action observation and imitation. These
findings suggest that categorization of complex dynamic
patterns may modulate processing in areas implicated in the
analysis of visual motion and actions.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-188Categorization of complex dynamic patterns in the human brain1501715422JastorffKG20057JJastorffZKourtziMAGieseTübingen, Germany2005-02-001318th Tübingen Perception Conference (TWK 2005)Learning has been proposed to contribute to the recognition of biological movements. We have investigated the neural correlates of such learning processes using event-related fMRI adaptation. This paradigm entails repeated presentation of a stimulus resulting in a decrease of the fMRI resonse, compared to stronger responses after a change in a stimulus dimension. This stronger response indicates sensitivity of the measured neural populations to this changed dimension. Novel biological movements were generated by linear combination of triples of prototypical trajectories of human movements. Subjects had to discriminate between identical, very similar, moderately similar and completely different point-light stimulus pairs. The difficulty of the discrimination task could be precisely controlled by choosing appropriate weight
vectors of the prototypes in the linear combinations. Subjects were able to learn the discrimination between these novel biological motion stimuli. The fMRI results indicate that several visual areas are involved in this learning process. More specifically, lower-level motion-related areas (hMT+/V5 and KO/V3B) show an emerging sensitivity for the differences between the discriminated stimuli, and higher-level areas (STS and FFA) show an increase of sensitivity after training. In addition, we find an overall reduction of the BOLD activity after training. Our present work focuses on modeling these BOLD signal changes during discrimination learning using a hierarchical physiologically-inspired neural model for biological motion recognition [1]. We show that learning of novel templates for complex movement patterns, encoded by
sequences of body shapes and optic flow patterns, can be implemented by hebbian learning. Our model combines competitive and time-dependent hebbian plasticity in order to establish new spatio-temporal templates exploiting physiologically plausible local learning rules. Our
results demonstrate that these mechanisms can account for the emerging sensitivity for novel movement patterns observed in fMRI. We conclude that our model provides a first step to formulate and test quantitative hypotheses about the neuronal plasticity mechanisms that underlie
the learning of complex biological and non-biological movement patterns.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-131Learning of Biological Motion: Combining fMRI and Theoretical Modeling1501715422McDonaldK20057SMcDonaldZKourtziTübingen, Germany2005-02-001848th Tübingen Perception Conference (TWK 2005)Our visual perception often differs from the physical reality of the natural world. We exploited this discrepancy, with a perceptual illusion known as motion induction, to examine motion processing of naturalistic stimuli in the human visual cortex. When an incoherently moving stimulus is placed in a coherently moving surround, observers perceive the incoherent pattern moving in the opposite direction to the surround. We used psychophysics and fMRI to investigate the neural basis of motion induction for naturalistic images. Specifically, we used
natural texture stimuli with 1/f amplitude spectra that consisted of a central region in a moving surround. The surround moved up or down with 100% coherent motion. We manipulated the coherence of the motion of the center: the center moved (up or down) at different coherence levels between random and 100%. When tested psychophysically, subjects misreported the direction of motion of the center. When the center had 0% coherence, observers perceived it
moving in the opposite direction to the surround. The observers’ point of subjective equality (PSE), i.e. when observers reported the center moving up and down an equal number of times, occurred when it had 30–50% coherent motion in the same direction as the surround. Based
on the physical properties of the stimulus, we predicted that fMRI responses would be lower at 0% coherence than at the PSE where the motion coherence is higher. Alternatively the perceptual results predicted that the difference between these two conditions would be absent, or even reversed. That is; stronger fMRI responses would be observed at 0% coherence where there is more perceived motion than at the PSE. Our results in hMT+/V5 showed that fMRI responses correlate with the perceptual rather than the physical coherence in the stimulus. Our findings suggest that the motion induction effect can be mediated by a combination of motion coherence and motion contrast mechanisms in hMT+/V5.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-184Perception of Motion Induction for Naturalistic Images in the Human Visual Cortex1501715422AltmannGKBK20057CAltmannWGroddZKourtziHHBülthoffH-OKarnathTübingen, Germany2005-02-001228th Tübingen Perception Conference (TWK 2005)Early neuropsychological observations described a patient that presented with impaired knowledge of object orientation but spared object recognition skills [1]. Similar cases exhibiting this peculiar dissociation have been reported since Best’s discovery. Interestingly, a recent study observed a double dissociation between object identification and orientation [2]. These findings were interpreted as evidence that separate cortical centers underlie visual object recognition and processing of spatial features. Accordingly, visual object perception has been suggested to follow two different routes in the human brain: a ventral, view-invariant occipital-temporal route
processes object identity, whereas a dorsal, view-dependent occipital-parietal route processes spatial properties of an object. Using fMRI, we addressed the question whether these routes are exclusively involved in either object recognition or representation of object orientation. To
this end, we presented subjects with images of natural objects and involved them either in an object identification or object orientation judgment task. For both tasks we observed activation in ventro-temporal as well as parietal areas bilaterally, with significantly stronger responses for the orientation judgment in ventro-temporal areas. Our findings suggest that object identification and orientation judgment do not follow strictly separable cortical pathways, but rather involve both the dorsal and the ventral stream.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-122Similar Cortical Correlates Underlie Visual Object Identification and Orientation Judgment1501715422KourtziALMK20047ZKourtziMAugathNKLogothetisJAMovshonLKiorpesSan Diego, CA, USA2004-10-0034th Annual Meeting of the Society for Neuroscience (Neuroscience 2004)Perceptual integration is critical for perception and interpretation of the visual world. Psychophysical studies suggest that these integrative processes for global form and motion develop slowly: when spatial resolution and contrast sensitivity approach adult levels (6-9 months in monkeys), global form and motion perception are still immature. The goal of this study was to investigate the neural development of perceptual integration by using fMRI on anesthetized macaques at different developmental stages. We examined the functional development of higher extrastriate visual areas whose delayed development might be responsible for the late maturation of coherent form and motion perception. We used Glass patterns, random dot patterns in which global structure is defined by the spatial or spatio-temporal orientation of correlated dot pairs to form contour and motion stimuli with identical local statistics but different global forms (e.g. radial, concentric). To compare form and motion processing directly, we used static and dynamic (patterns with both spatial and temporal offset between dots) Glass patterns to activate the ventral and dorsal pathways, respectively. We compared fMRI responses for static and dynamic Glass patterns to those for static and dynamic random noise patterns. Experiments in adult macaques showed stronger activations for static Glass than random patterns in ventral extrastriate visual areas, whereas stronger activations for dynamic Glass than random patterns were observed in dorsal motion areas. Longitudinal study of two infant monkeys from the age of 8 months showed some differential activation for dynamic than random patterns but not for static Glass patterns. These results are consistent with previous perceptual and neurobiological evidence that the dorsal extrastriate pathway develops more quickly than the ventral pathway.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published0Development of global form and motion perception in monkeys studied with fMRI15017154221501715421MoutoussisKKL20047KMoutoussisGKelirisZKourtziNKLogothetisSan Diego, CA, USA2004-10-0034th Annual Meeting of the Society for Neuroscience (Neuroscience 2004)The relationship between brain activity and conscious visual experience is central to our understanding of the neural mechanisms underlying perception. Binocular rivalry, where monocular stimuli compete for perceptual dominance, has been previously used to dissociate the constant stimulus from the varying percept. We report here fMRI results from humans experiencing binocular rivalry under a dichoptic stimulation paradigm that consisted of two drifting random dot patterns with different motion coherence. Each pattern had also a different color, which both enhanced rivalry and was used for reporting which of the two patterns was visible at each time. As the perception of the subjects alternated between coherent motion and motion noise, we examined the effect that these alternations had on the strength of the MR signal throughout the brain. Across the different visual areas, we have found varying degrees of correlation between the neural activity and the visual percept. Areas V3A, V5 (MT) and LOC showed a much stronger activation when subjects perceived coherent motion than when they perceived motion noise. A similar but not as strong an effect was observed in area V3, whereas a much less pronounced difference between the two conditions was found in areas V1, V2 and V4. These results demonstrate that motion perception is able to modulate the activity of most visual areas known to be involved in motion processing. Instead of a clear distinction between ‘processing’ and ‘perceptual’ areas, we found a gradual increase in the correlation between neural and perceptual events as one moves towards the higher areas of the motion pathway. We thus conclude that the areas involved in the processing of a specific visual attribute are also part of the neuronal network that is collectively responsible for its perceptual representation.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published0The involvement of different areas of the human visual brain in motion perception15017154211501715422MuckliWKSK20047LMuckliSWeigeltAKohlerWSingerZKourtziBudapest, Hungary2004-06-00e1025e102710th Annual Meeting of the Organization for Human Brain Mapping (HBM 2004)Introduction
For a successful interaction with our environment it is necessary to gather information about form and motion of
objects. Form and motion is, however, processed along specialized pathways. Here, we focused on the
interactions between form and motion processing in the context of an object apparent motion paradigm called
apparent rotation (1).
Methods
We presented in rapid succession a perspective view of a three-dimensional object and a rotated version of the
same object (Fig. 1). Herby we induced the illusion of a rigid 3D-object rotation (apparent rotation). It has been
proposed on grounds of priming experiments that the intermediate rotation positions are explicitly represented in
the visual system (2). To find regions involved in the explicit representation of the illusory rotation path we
designed a functional magnetic resonance imaging experiment using an adaptation design (fMRI-A) (3). In an
event-related fMRI-A experiment at 3Tesla (TR=1s, TE=40ms, FA=60°, voxel size= 3 x 3 x 5 mm3 ) we
presented first a pair of visual stimuli to induce the apparent rotation illusion (object and rotated object), followed
by one of five test stimuli consisting of the same object rotated in space. A test stimulus was either a repetition of
the second position (repeated, maximal adaptation), a stimulus rotated to an intermediate position (intermediate,
possibly adapted), two extrapolated positions (continuous and reverse extrapolation) not on the rotation path
(minimal or no adaptation), and an object that was rotated along an additional axis (novel, not adapted) (Fig. 1).
For a region that combines motion and object information we predict adaptation of activation for the presented
objects, and for those that are on the rotation path (predicted adaptation profile: repeated < intermediate <
continuous extrapolation < reverse extrapolation = novel). Subjects classified the test objects to be rotated
versions of the same or of a different object. We used BrainVoyager™ for stimulus generation and data analysis.
Results
We found two regions with an activation profile that indicated adaptation for the presented objects and for the
interpolated illusory objects (Fig. 2): one in the intraparietal sulcus (IPS +/-30, -68, 17) and another around the
anterior part of the insula (+/-32, 16, 10) in the frontal lobe. In both regions the BOLD-response to the
intermediate stimulus (red) and the repeated one (orange) was significantly lower than to the stimuli, which lay
outside the apparent motion path (continuous [blue] and reverse extrapolation [turquoise], novel [green]).
Psychophysical data: The continuous extrapolated stimulus is less often recognized as a rotated version of the
same object than the intermediate stimulus (Fig. 3), although both are rotated for the same amount. We can
conclude therefore that subjects recognized adapted objects more easily.
Conclusion
We conclude that IPS and INS play an important role in combining object and motion properties. In future
experiments we will try to replicate our results in the context of an additional centre task.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published0Apparent Rotation: fMRI-Adaptation of the Illusory Rotation Path150171542233287KMoutoussisGAKelirisZKourtziNKLogothetisBudapest, Hungary2004-06-00e1023e102410th Annual Meeting of the Organization for Human Brain Mapping (HBM 2004)Introduction
One of the most fascinating problems in visual neuroscience is finding a direct relationship between brain activity
and perception. When a visual stimulus is presented to the eyes, it elicits a series of responses in many and
different parts of the visual system, from the retina to the ’higher’ cortical areas, leading to a conscious visual
percept. Dissociating which part of the visual brain activity is reflecting our perception is thus hard, since at the
same time this activity is directly related to the processing of the visual stimulus itself. To try and answer this
question, binocular rivalry has been used in the past, where the stimulus (which is different for each eye) remains
constant but the perception alternates between the two rivalring monocular inputs. In this way one can dissociate
the stimulus from the percept and, by studying the alternations in brain activation under such conditions, get an
insight into which brain areas correlate their activity with what the subject actually perceives.
Methods
Binocular rivalry was used in fMRI experiments that were performed on a Siemens Trio 3T system. A different
random dot kinematogram was shown to each eye, one consisting of red and the other of green dots. In one of the
kinematograms 50% of the dots moved in the same direction producing a coherent motion signal whereas in the
other all dots moved in random directions thus producing pure motion noise. As binocular rivalry developed
between red dots in one eye and green dots in the other, subjects inside the scanner used two different buttons to
report whether they perceived one the another color. In this way we could relate the BOLD signal we recorded in
the magnet to the subjects’ percept and investigate how motion perception is reflected in the cortical activation of
the various visual areas.
Results
Averaging the event-related time-courses across all subjects showed a range of different responses, with no
significant effect in areas V1, V2 and V4, only a slight difference in area V3, and a much more clear difference in
areas V3a, V5 and LOC (Fig. 1).
Discussion
In this study we were able to show that a number of visual areas are involved in motion perception. In general, the
more involved an area is in motion processing, the more it is modulated by motion perception, supporting the idea
that processing and perceptual areas are not distinct and separable, but rather the same areas are involved in both
processing and perception.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published0Neural correlates of motion perception in the human visual brain1501715421AltmannK20047CFAltmannZKourtziBudapest, Hungary2004-06-00e90410th Annual Meeting of the Organization for Human Brain Mapping (HBM 2004)Successful interactions in our dynamic environment require that the visual system processes the shape, the
3D-structure and the motion of objects. Different cortical areas have been proposed to be involved in the
processing of visual motion (hMT+/V5 = human middle temporal homologue), kinetic boundaries (V3B/KO =
kinetic occipital), depth information (V3A) and object shape (LOC = lateral occipital complex). The goal of this
study was to investigate whether these areas are selective for the 3D-structure of shapes defined by coherent
motion and horizontal disparity information.
To this end, we conducted two human fMRI experiments at a Siemens TRIO 3T MRI facility in which we used an
event-related fMRI adaptation paradigm. In this paradigm, lower fMRI responses are observed for two identical
than for two different stimuli that are presented consecutively in a trial. Adaptation across a change between two
stimuli provides evidence for a common neural representation invariant to that change, while recovery from
adaptation suggests neural representations selective for specific stimulus properties. We employed stimuli in
which shapes were defined by the relative motion of random dots in the shape and the background. Additionally,
the 3D-structure of these shapes was defined by the horizontal disparity of the random dots.
In our first study, we tested whether shape and motion related areas are either selective for the 3D structure of
shapes defined by horizontal disparity or for their outline. To this end, we tested four conditions: a) Identical, b)
Different 3D-structure (Concave/Convex), c) Different shape outline, d) Different 3D-structure and shape outline.
Recovery from adaptation was observed across changes in 3D structure in V3B/KO, hMT+/V5 and the LOC.
Changes in the shape outline resulted in increased fMRI responses in hMT+/V5 and the LOC.
These results suggest selectivity for 3D-shape in both shape (LOC) and motion-related areas (hMT+/V5).
In a second study, we tested whether selectivity for the 3D structure of shapes can be simply accounted by
differences in local disparities or by selectivity for global 3D-structure. To this end, we presented subjects with
correlated and anti-correlated random dot stereograms, which contain horizontal disparity information but do not
induce the perception of 3D-structure. Specifically, we tested for fMRI responses in four conditions: a) same
disparity without 3D-structure b) different disparity without 3D-structure, c) same disparity and different
3D-structure b) different disparity and different 3D-structure. Selectivity for both local disparity information and
global 3D-structure was observed in shape-related areas (V4v, LOC) as well as in motion-related areas (V3B/KO,
hMT+/V5). In contrast, early visual areas (V1, V2, VP) showed selectivity for local disparity only.
In summary, our findings provide conclusive evidence that not only shape (LOC) but also motion-related areas
(hMT+/V5, V3B/KO) are involved in the selective representation and perception of the global 3D-structure of
shapes.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published0Processing of the perceived 3D-structure of objects in the human visual cortex1501715422JastorffKG20047JJastorffZKourtziMGieseGiessen, Germany2004-04-0012646. Tagung Experimentell Arbeitender Psychologen (TeaP 2004),nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-126fMRI adaptation dissociates multiple areas involved in biological motion recognition15017154221501715421HuberleK20047EHuberleZKourtziTübingen, Germany2004-02-001367th Tübingen Perception Conference (TWK 2004)Coherent visual perception requires the integration of local elements into global shapes. However,
the involvement of the various visual areas in the integration of local features into global
shapes remains largely unknown.Event-related fMRI was used to test for local and global
mechanisms of shape processing in higher visual object related areas. We tested for responses
in the Fusiform Face Area (FFA) known to respond selectively to faces [1] and the Parahippocampal
Place Area (PPA) known to be involved in the analysis of spatial layout [2]. The
stimuli consisted of images of houses or faces (global shapes) rendered by smaller images of
stimuli from these categories (local shapes). We tested four conditions: a) global faces rendered
by local faces; b) global faces rendered by local houses; c) global houses rendered by local
faces and d) global houses rendered by local houses. Subjects were instructed to judge whether
global and local shapes where from the same or different categories. Our results showed strong
fMRI responses for global faces in the FFA and global houses in the PPA independent of the
stimulus category at the local level. Lower category specic responses to the local shapes were
observed when the global shapes were from a different category than the local shapes. Further
studies tested for fMRI responses at different stimulus scales and attentional shifts. Stronger
responses to the local faces in the FFA and local houses in the PPA were observed compared
to global faces and global houses. Our results suggest differential processing of global and
local shape information in category selective areas. Furthermore, attention and spatial scale
inuence the processing of local and global shape information.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-136Global and Local Mechanisms of Shape Processing in the Human Visual Cortex1501715422JastorffGK2004_27JJastorffMAGieseZKourtziTübingen, Germany2004-02-001377th Tübingen Perception Conference (TWK 2004)Introduction: Previous experimental work indicates that biological motion recognition is dependent
on learning. In order to determine neural correlates of this learning process we conducted
an fMRI adaptation experiment (cf. [1]). Compared to previous studies using a classical
block design, adaptation experiments have the advantage that they allow to distinguish multiple
functionally distinct neural subpopulations within the same voxel, exploiting the fact that the
BOLD signal decays if the same stimulus is presented repeatedly. Methods: Pairs of unfamiliar
motion stimuli for a discrimination task were generated by motion morphing between triples of
prototypical trajectories of human movements. The morphs were generated by linear combination
of the prototypical trajectories in space-time [2]. Subjects had to discriminate between
two successive stimuli presented as Johansson point light walkers with same or different linear
weights of the prototypes. By choosing appropriate weight vectors the difculty of the discrimination
task can be precisely controlled. This was used to generate four conditions with identical
(SAME), very similar (SIMILAR), moderately similar (DISSIMILAR), and completely
different (DIFFERENT) stimulus pairs. Subjects reported whether they perceived the successive
stimuli as same or different. The subjects were scanned before and after a training period.
Areas relevant for the processing of biological motion (early visual areas, MT+ , KO, FFA,
and STS) were localized using standard techniques. Results: Before the training subjects could
discriminate the stimuli in the DISSIMILAR and in the DIFFERENT condition. After training
they could also discriminate the stimulus pairs in the SIMILAR condition. Comparing the
BOLD signal before and after the training period we found a signicant reduction of the signal
in all localized regions of interest. Before training, we obtained signicant adaptation effects
for the SAME and the SIMILAR condition only in area FFA and the STS. The other areas did
not show selective adaptation. After training, however, no adaptation effect was observed for
the SIMILAR condition any more. This result is consistent with an increased discrimination
capability after training. Conclusion: We have successfully established the fMRI adaptation
paradigm for biological motion experiments. The adaptation effects in area FFA and the STS
are consistent with the discrimination performance of the subjects before and after training.
Conforming with earlier studies, the STS and area FFA seem to be critical for biological motion
recognition. The general decrease in BOLD signal observed after training might be related
to a more efcient encoding of the stimuli after learning.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-137Neural Correlates of the Learning of Biological Motion: An fMRI Adaptation Experiment1501715422150171542125107CFAltmannZKourtziTübingen, Germany2004-02-00987th Tübingen Perception Conference (TWK 2004)Interactions in our dynamic environment require that the visual system processes both the shape
and motion of objects. Different cortical areas have been proposed to be involved in the processing
of visual motion (hMT+/V5 = human middle temporal homologue), kinetic boundaries
(KO = kinetic occipital) and object shape (LOC = lateral occipital complex). The goal of this
study was to investigate whether these areas are involved in the perception of shapes dened
by motion coherence. To this end, we used human event-related fMRI and employed stimuli
in which the shape was dened by the relative motion of random dots in the shape and the
background. We manipulated the perception of these shapes by independently varying the motion
coherence of the dots in the shape and the background. Increased motion coherence in
either the shape or the background improved the behavioral performance of the observers in a
shape categorization task. FMRI responses in the LOC and KO were consistent with the behavioral
performance; that is, enhanced fMRI responses were observed with increased motion
coherence in either the shape or the background. Interestingly, hMT+/V5 showed activation
patterns similar to the LOC, suggesting strong interactions between ventral (LOC) and dorsal
(hMT+/V5) visual areas in the perception of shape from motion. To further investigate shape
representations from motion in the different visual areas we tested for selectivity for shape and
motion direction information. To this end, we used an fMRI adaptation paradigm in which
lower fMRI responses are observed for two identical than two different stimuli presented consecutively
in a trial. Recovery from adaptation was observed across changes in shape in the
LOC, KO, and hMT+/V5, but not in early visual areas. In a third study, we tested whether
shape and motion related areas are selective for the 3D structure of shapes. To this end, we
employed an fMRI adaptation paradigm and similar stimuli as in the two previous studies. In
addition, these stimuli were rendered with 3D structure using horizontal disparity cues. Recovery
from adaptation was observed across changes in 3D structure in the LOC, KO, and
hMT+/V5. In summary, these ndings suggest that not only object (LOC) but also motionrelated
areas (hMT+/V5) are involved in the selective representation and perception of shapes
dened by coherent motion.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-98Processing of Shape from Coherent Motion in the Human Visual Cortex150171542226187CDahlMGrafMErbZKourtziWGroddHHBülthoffTübingen, Germany2004-02-001017th Tübingen Perception Conference (TWK 2004)How is basic level categorization achieved in the human brain? Deforming shape (morphing)
transformations are well suited to describe the shape variability of members of common basic
level categories. Behavioral experiments showed that categorization performance deteriorates
systematically with increasing amount of morph transformation [1, 2]. A possible explanation
for these ndings is that categorization relies on time-consuming compensation processes
(deformable template matching). If spatial compensation processes are involved, then categorization
might not only comprise the ventral visual pathway, as generally assumed, but also the
dorsal stream. We investigated this question with functional MRI.
Objects from 25 common basic level categories were generated by morphing between two
members of the same category (using 3ds max). Eleven subjects participated in two tasks,
starting with the categorization task. Subjects had to decide as fast as possible whether two
sequentially presented objects belonged to the same basic level category. The transformational
distance between category members was varied (event-related design). In a second task,
the same observers perceived intact morphing sequences, scrambled morphing sequences, and
static presentations of different morph exemplars (block design). fMRI data were acquired on a
3T scanner (Siemens Trio), measuring 24 slices of 64x64 voxels every two seconds (resolution
of 3x3x5 mm
A
).
In the categorization task, the response latencies for same trials increased with increasing
morph distance between two category members. Correspondingly, the contrast long vs. short
morph distance revealed an increasing BOLD signal in LOC (lateral occipital complex). Moreover,
activation increased also in the superior parietal cortex (BA 7) and in the frontal cortex
(BA 44). Control analyses showed that this pattern of activation cannot be reduced to task
difculty, or increasing dissimilarity between the objects. In the second task we found dorsal
activation for the comparison between intact vs. scrambled morphing sequences. This activation
spot was close to the dorsal activation in the categorization task, but was not identical.
The results suggest that basic level categorization is not limited to the ventral pathway,
but rather relies on a network of ventral, dorsal and frontal activation. The activation within
this network is systematically dependent on the amount of shape transformation. The dorsal
activation seems related to compensational processes taking place in parietal cortex, i.e. spatial
(deforming) transformation processes. These ndings are in accordance with an alignment
approach of object recognition and categorization.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-101Shape Processing in Basic Level Categorization: An fMRI Investigation150171542223847ADeubeliusAEWelchmanZKourtziNKLogothetisNew Orleans, LA, USA2003-11-0033rd Annual Meeting of the Society for Neuroscience (Neuroscience 2003)Humans can perceive object shape based on a range of different sources of visual information (or cues). Two cues to shape, that the visual system appears to be especially sensitive to, are horizontal binocular disparity and geometric perspective. This study examined the relationship between fMRI activity in the human brain and the perception of shape from perspective and disparity cues. Observers viewed open book stimuli consisting of a hinged plane receding symmetrically in depth. We parametrically varied the dihedral angle between the planes. Observers were required to judge which dihedral angle was larger (or more open) of two sequentially-presented stimuli. Stimuli were rear-projected inside a 3T scanner. Psychophysical judgments were made whilst fMRI responses were collected concurrently. We employed an event-related fMRI adaptation paradigm in which stimulus changes result in increased fMRI responses (rebound effect) compared with repeated presentation of the same stimuli. Psychophysical data were fit using Probit analysis and the perceptual discriminability of different stimuli was calculated. We examined fMRI responses in early retinotopic visual areas, higher object-related (Lateral Occipital Complex-LOC) and motion-related (hMT+/V5) areas. We observed significant fMRI rebound effects, that is increased responses compared with repeated presentation of the same stimulus, in early and higher visual areas. These rebound effects were consistent with the discriminability of the perceived shape in areas LOC hMT+/V5. These results suggest that both object and motion-related visual areas are involved in the perception of 3D shapes from multiple visual cues.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de//fileadmin/user_upload/files/publications/pdf2384.pdfpublished0An fMRI parametric study of shape from disparity and perspective in the human visual cortex15017154211501715422LestouPK20037VLestouFEPollickZKourtziNew Orleans, LA, USA2003-11-0033rd Annual Meeting of the Society for Neuroscience (Neuroscience 2003)The neuronal system involved in action understanding and imitation, involves the ventral premotor cortex (Ba44), parietal areas and the Superior Temporal Sulcus (STS). Neuroimaging and neurophysiological studies implicate the ventral premotor cortex in the processing of action goals while the function of the remaining areas is largely unknown. The present study investigated whether the goal and the kinematics of the movement are differentially processed within these cortical areas. We used an event-related fMRI adaptation paradigm, in which fMRI responses to two sequentially repeated stimuli are lower than for different stimuli. Using kinematics morphs (Hill & Pollick, 2000) we tested the hypothesis that the premotor cortex in humans processes information about the goal of an action while parietal regions code for the kinematics of the movement. Four different action types and their kinematics morphs were used for the experiments. We functionally localised the brain areas involved in action understanding and imitation. We then tested for fMRI responses in the different experimental conditions during the event related scans. In the first series of experiments we showed that the premotor cortex represents the goal of the movements independent of their kinematics. Adaptation effects were observed across changes in the movement kinematics in the premotor cortex but not in parietal regions. These results suggest that the premotor cortex represents the goal of movements independent of their kinematics, while parietal regions encode information about the movement kinematics. Surprisingly, adaptation effects in hMT+/V5 and STS were similar to these in the premotor cortex. No differences across conditions were observed in early visual areas (i.e. V1). Subsequent experiments tested fMRI responses when the kinematics of the action remained the same while the goal of the action changed.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published0Differential involvement of prefrontal and parietal areas in human imitation revealed by fMRI adaptation150171542223497AEWelchmanADeubeliusZKourtziNew Orleans, LA, USA2003-11-0033rd Annual Meeting of the Society for Neuroscience (Neuroscience 2003)The visual system is sensitive to multiple visual cues indicating the shape of objects; these cues are combined by the brain to result in unified shape perception. The goal of this study was to examine whether different visual areas are involved in the analysis of individual cues versus the representation of the perceived shape based on combined cues. We manipulated horizontal binocular disparity and geometric perspective cues to the shape of test stimuli (hinged planes). Disparity and perspective cues could indicate the same shape (consistent cues) or different shapes (inconsistent cues). Psychophysical judgments about the angle between the hinged planes of two sequentially-presented stimuli were collected concurrently with fMRI responses. A sequential-presentation fMRI adaptation paradigm was employed, in which stimulus changes result in increased fMRI responses (rebound effect) compared with repeated presentation of the same stimuli. We used conditions in which either individual cues changed, or both cues changed. We tested for fMRI responses in early retinotopic visual areas, higher object-related (Lateral Occipital Complex-LOC) and motion-related (hMT+/V5) areas. We observed significant fMRI rebound effects in early and higher visual areas. These rebound effects followed similar patterns to psychophysical discrminiability (d prime) of the perceived shape in areas LOC and hMT+/V5. However, rebound effects in areas V3 and V3a were consistent with changes in each of the individual cues rather than the perceived shape per se. These results suggest that early visual areas are involved in cue-based representations, while representations based on a combination of cues appear to be encoded in higher object-related (LOC) and motion-related (hMT+/V5) areas.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published0Perceptual versus cue-based shape representations in the human visual brain1501715422HuberleK20037EHuberleZKourtziNew Orleans, LA, USA2003-11-0033rd Annual Meeting of the Society for Neuroscience (Neuroscience 2003)Coherent visual perception requires the integration of local elements into global shapes. However, the involvement of the various visual areas in the integration of local features into global shapes remains largely unknown. We used event-related fMRI to test for local and global shape processing in visual areas known to be involved in the processing of shapes. The stimuli consisted of images of houses or faces (global shapes) rendered by smaller images of stimuli from these categories (local shapes). We tested four conditions: a) global faces rendered by local faces; b) global faces rendered by local houses; c) global houses rendered by local faces and d) global houses rendered by local houses. Subjects were instructed to judge whether global and local shapes where from the same or different categories. We tested for responses in the Fusiform Face Area (FFA) known to respond selectively to faces (Kanwisher et al., 1997) and the Parahippocampal Place Area (PPA) known to be involved in the analysis of spatial layout (Epstein et al., 1998). Our results showed strong fMRI responses for global faces in the FFA and global houses in the PPA independent of the stimulus category at the local level. Lower category specific responses to the local shapes were observed when the global shapes were from a different category than the local shapes. These results suggest differential processing of global and local shape information in category selective areas. Further studies will test for the processing of global and local shape information at different stimulus scales.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published0Processing of global vs. Local shape information in the human visual cortex150171542231877LRBettsPSarkheilZKourtziNew Orleans, LA, USA2003-11-0033rd Annual Meeting of the Society for Neuroscience (Neuroscience 2003)The aim of this study was to investigate the effect of learning in the integration of local elements into coherent visual shapes. Human early (V1, V2, VP, V4) and higher visual areas known to be involved in the analysis of shape information (Lateral Occipital Complex-LOC) have been implicated in the perceptual integration of global shapes. We used event-related fMRI to investigate the effect of learning in the neural representation of shapes across the human visual cortex. The stimuli consisted of symmetrical and asymmetrical closed contours rendered by aligned gabor elements and embedded in random gabor background fields. Two stimuli were presented simultaneously in each trial to the left and right of the fixation point and the subjects were instructed to report which stimulus contained the symmetrical contour. Behavioral and fMRI responses were recorded while observers performed the 2-AFC shape discrimination task in two different sessions, one before and one after three days of training. Observers were shown different sets of novel stimuli in every session and a set of training stimuli rendered in novel backgrounds across trials. Prior to training, no differences were observed in the behavioral performance or the fMRI responses across visual areas for the novel vs. the training stimulus set. However, after training the observers showed significantly improved accuracy in the discrimination task for learned vs. novel shapes. Consistently, fMRI responses in the early and the higher visual areas were significantly stronger for learned than novel stimuli. These results provide evidence for behavioral and neuronal learning-based plasticity in the human visual areas involved in coherent shape perception.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published0Psychophysical and fMRI measures of shape learning in the human visual cortex15017154221501715421TjanLBK20037BSTjanVLestouHHBülthoffZKourtziSarasota, FL, USA2003-10-00109Third Annual Meeting of the Vision Sciences Society (VSS 2003)Visual processing in the human ventral cortex entails extraction of features from retinal images that mediate perception. In the human ventral cortex, early and late visual areas have been implicated in the analysis of simple and complex features respectively. If we view this processing pathway as a sequence of decision stages, each extracting progressively more abstract and invariant features from the output of preceding stages, then by considering the relationship between signal uncertainty and the slope of a psychometric function, we can show that the extent to which the output of a decision stage is perturbed by noise added to the visual stimulus will be more threshold-like (steeper log-log slope) for a decision stage further down the decision cascade. To test this theory, we used images of scenes and added visual noise that matched the signal's spatial-frequency power spectrum. The resulting images were rescaled to maintain a constant mean luminance and rms contrast across all noise levels. We localized individually in each observer the retinotopic regions and the LOC, and measured event-related BOLD response in these regions during a scene discrimination task performed at 4 noise levels. Behavioral performance increased with increasing signal-to-noise ratio. We found that log %BOLD signal change from fixation baseline vs. log SNR is well-described by a straight line for all visual areas. The regression slope increased monotonically from early to late areas along the ventral stream. A factor of 8 change in SNR produced little change to the BOLD response in V1/V2, but resulted in progressively larger changes in V4v, posterior (LO), and anterior (pFs) subregions of the LOC. In accordance with our theory on noise perturbation, the results suggest approximately ordered decision stages in the ventral pathway.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-109An fmri method for identifying the sequential stages of processing in the ventral visual pathway150171542221097AEWelchmanADeubeliusSJMaierHHBülthoffZKourtziSarasota, FL, USA2003-10-00850Third Annual Meeting of the Vision Sciences Society (VSS 2003)Recent models of cue combination (e.g. Landy et al., 1995, Vis Res, 35, 389) suggest that the perception of an objects 3D shape is mediated by the combination of different depth cues (e.g. disparity and texture). We used fMRI to investigate the neural substrates of this process. Methods: Vertical cylinders defined by binocular disparity and texture cues were rear-projected inside a 3T scanner. We studied cylinders in which both disparity and texture specified the same curvature (consistent cues), and cylinders in which the two cues specified different curvatures (inconsistent cues). Prior to conducting fMRI experiments, subjects adjusted the curvature of consistent cue cylinders so that their perceived curvature was similar to that of the inconsistent ones. Performance in this task was used to define stimuli with consistent cues that were perceived to have similar curvature to the inconsistent cue stimuli. We employed a sequential-presentation fMRI adaptation technique, in which stimulus changes result in increased fMRI responses compared with repeated presentation of the same stimuli. Results: We observed increased responses in the Lateral Occipital Complex (LOC) and hMT(V5)+ when the subjects discriminated curvature changes. In contrast, adaptation in these regions was observed when subjects perceived similar curvature. Conclusions: These findings suggest that visual areas LOC and hMT(V5)+ are involved in the processing of perceived 3D shape based on the combination of disparity and textures cues.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-850fMRI correlates of visual cue combination1501715422KourtziTAAL20037ZKourtziASToliasCFAltmannMAugathNKLogothetisSarasota, FL, USA2003-10-00191Third Annual Meeting of the Vision Sciences Society (VSS 2003)The perception of global visual shapes entails the integration of local image features into global configurations. Traditionally, the visual system is thought to be hierarchically organized in early visual areas (V1, V2, V3, V4) that are involved in the analysis of simple local features and higher visual areas (regions in the inferotemporal cortex) that are implicated in the processing of complex global shapes. We investigated the integration of local image features into global shapes across visual areas in the monkey and the human brain using fMRI. An adaptation paradigm was used, in which stimulus selectivity was deduced by changes in the course of adaptation of a pattern of randomly oriented elements. Accordingly, we observed stronger activity after adaptation when orientation changes in the adapting stimulus resulted in a collinear shape than a different random pattern. This selectivity to collinear shapes was observed not only in higher visual areas, but also in early visual areas where selectivity depended on the receptive field size. These findings suggest that unified shape perception in both monkeys and humans involves multiple visual areas that may integrate local elements to global shapes at different spatial scales.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-191Integration of local features into global shapes: monkey and human fMRI studies15017154221501715421JastorffKG2003_27JJastorffZKourtziMAGieseSarasota, FL, USA2003-10-0084Third Annual Meeting of the Vision Sciences Society (VSS 2003)It has been shown, that humans can learn to discriminate between different styles of natural movements (e.g. gaits or sports movements). However, it remains unknown whether this learning is based on ‘innate’ templates for biological movement patterns, or if humans can learn new representations of arbitrary complex movements. We address this question by investigating, whether subjects can learn novel artificial biological movement stimuli. These stimuli were generated by linearly combining prototypical trajectories of very dissimilar natural movements in space-time using spatio-temporal morphable models (Giese & Poggio, 2000). Most of the tested stimuli do not correspond to naturally occurring movements, and some of them likely even violate the physical laws of human body movement. Subjects had to discriminate between pairs of these stimuli, containing slightly different weights of the prototypes. The stimuli were presented as standard point light walker (PLW), and as point light walker with position jitter (generated by adding random displacements of the dots along the skeleton of the walker for every frame). Subjects trained with standard PLW learned relatively quickly (after about 8 trails) to discriminate between these stimuli. Testing different subjects with stimuli that were rotated by 90 deg in the image plane showed that the learned representation transferred to rotated stimuli. Subjects that were trained with PLW with position jitter learned the discrimination task equally fast (8 trials). However, another set of subjects trained with the same stimuli and tested with rotated stimuli did not show transfer of the learned discrimination to rotated stimuli. We draw the following conclusions from this experiment: (1) New templates for biological movement recognition can be acquired very quickly. (2) Learning affects at least two different levels of representation (local and holistic). (3) The learned holistic representations seem to be view-dependent.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-84Role of learning in biological motion recognition1501715422150171542121147EHuberleADeubeliusWLutzenbergerHHBülthoffZKourtziSarasota, FL, USA2003-10-00266Third Annual Meeting of the Vision Sciences Society (VSS 2003)Recent studies have shown that global information about shapes is processed in both early ventral (i.e. V1, V2, Vp, V4) and higher occipitotemporal visual areas (i.e. Lateral Occipital Complex-LOC). However, the temporal properties of shape processing across visual areas in the human brain are not known. We addressed this question in a combined fMRI and MEG study that made use of the complimentary spatial and temporal resolution of the two techniques. We used an event-related adaptation paradigm in which lower neural responses are observed for two identical than two different consecutively-presented stimuli. The stimuli were closed contours that consisted of collinear Gabor elements. We manipulated the interstimulus interval (ISI: 100 vs. 400 msec) between the two consecutively-presented stimuli. The fMRI results showed adaptation for both the short and the long ISI in the LOC but only for the short ISI in early visual areas. The MEG data showed similar patterns of response amplitude to the fMRI data and differences in latencies for the different ISIs across visual areas. These findings suggest sustained shape processing in higher visual areas compared to more transient visual analysis in early visual areas. Further studies test the analysis of local vs. global shape features across areas with different temporal processing properties.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de//fileadmin/user_upload/files/publications/pdf2114.pdfpublished-266Temporal properties of shape processing across visual areas: a combined fMRI and MEG study1501715422LestouPBK20037VLestouFEPollickHHBülthoffZKourtziSarasota, FL, USA2003-10-00525Third Annual Meeting of the Vision Sciences Society (VSS 2003)The perception and imitation of human movement requires that the brain integrates information about the goal of the movement and the kinematics that define it. Neuroimaging and neurophysiological studies implicate the ventral premotor cortex (Ba44) in the processing of action goals while the role of the parietal cortex is not entirely clear. The aim of this series of experiments was to disentangle the role of both prefrontal and parietal areas in the imitation of human movement. To this end we used human arm movements presented as point light displays. The movements were manipulated parametrically to produce morphs that differed from each other in their kinematics. Three different action types -throwing, lifting and knocking movements- and their morphs were utilised for this study. We used a rapid event related fMRI adaptation paradigm, in which fMRI responses to two sequentially repeated stimuli are lower than for different stimuli. We begun by functionally localising the brain areas involved in the imitation of human movement. We then looked at the MR signal under the different experimental conditions during the event related scans. In a first experiment we investigated the basic adaptation effect; identical movements both in their action goals and kinematics were tested against movements that were different in both their goals and kinematics. Preliminary evidence suggests that prefrontal and parietal areas show adaptation under those different experimental conditions. Future experiments will test whether the parietal areas respond to different kinematics even when the goal of the movement is the same, by using the kinematics morphs.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-525The involvement of parietal and prefrontal areas in human imitation revealed by fMRI adaptation1501715422JastorffKG20137JJastorffZKourtziMAGieseGöttingen, Germany2003-06-006265th Meeting of the German Neuroscience Society, 29th Göttingen Neurobiology ConferenceHuman body motion presented as point-light stimuli can be readily recognized. Psychophysical experiments show that these impoverished stimuli are sufficient for the discrimination between different actions and even for the extraction of the gender and other details of the moving actor. Additionally, a few studies indicate the capability of humans to learn to discriminate different styles of natural movements (e.g. gaits or sports movements).
However, it remains unknown whether this learning is based on innate templates for biological movement patterns, or if humans can learn new representations of arbitrary complex movements. We address this question by investigating whether subjects can learn artificial biological movement stimuli.
Methods: The stimuli used in this study were generated by linear combination of prototypical trajectories in space-time using spatio-temporal morphable models (Giese &
Poggio, 1999). We created two different classes of stimuli: (A) Stimuli derived by linear combination of dissimilar natural movements (e.g. walking, kicking and dancing). (B)
Stimuli generated by animation of an artificial skeleton model that is highly dissimilar from naturally occurring body structures. The joint angle trajectories of the skeleton were given by linear combinations of synthetic sinusoidal trajectories. Their amplitudes and frequencies were approximately matched with the joint trajectories of human actors during natural movements. For both classes, several stimuli were created which served as prototypes for the morphing procedure. Subjects had to discriminate within one class between pairs of these stimuli that were
defined by linear combinations with slightly dissimilar weights of the prototypes. The trajectories were presented as normal point light walkers (PLW), and as point light
walker with position jitter (PLWJ). The PLWJ were generated by adding random displacements of the dots along the skeleton of the walker in each frame (similar to Beintema
& Lappe, 2002). Each subject took part in three test blocks that were intersected by two blocks of training. Feedback was provided only during training.
Results: Subjects trained with stimuli derived from natural movements (class A) learned the discrimination between novel patterns very quickly, regardless of the stimulus type
(PLW/PLWJ). If the training stimuli were rotated 90 deg in the image plane against the test stimuli, we observed transfer of the learned representation only for the normal PLW but not for the PLWJ stimuli. The completely artificial stimuli (class B) were only presented as PLWJ. Subjects were
able to learn these stimuli equally fast as the natural stimuli (class A). In addition, we found the same view dependence as for the natural stimuli.
Conclusions: (1) New templates for movement recognition can be learned very quickly. (2) Learning affects at least two different levels of representation (local and holistic). (3)
The learned holistic representations seem to be view-dependent. (4) There seem to be no significant differences between the learning process for stimuli derived from artificial and natural movements.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-626Learning of natural and synthetic biological motion150171542221067CFAltmannADeubeliusZKourtziHHBülthoffKiel, Germany2003-03-0015845. Tagung Experimentell Arbeitender Psychologen (TeaP 2003)Aktuelle Modelle der visuellen Objekterkennung schlagen eine hierarchische Verarbeitung visueller Informationen vor. Wenig geklärt ist jedoch, inwieweit höhere visuelle Areale bei der Figur-Grund-Segmentierung auch Kontextinformation repräsentieren. Um dieser Fragestellung nachzugehen, untersuchten wir den lateral okzipitalen Komplex (LOC), eine kortikale Struktur, die an der Verarbeitung von Objektinformation beteiligt ist, mithilfe eines fMRI-Adaptations-Paradigmas. Dieses macht sich zunutze, dass das fMRI-Signal bei visueller Stimulation nach mehrmaliger Präsentation gleichen Reizmaterials zurückgeht. Für den LOC irrelevante Reizänderungen sollten zu fMRI-Adaptation in dieser Struktur führen. Wir konnten beobachten, dass Kontextänderungen nicht in Adaptation resultierten, d.h. der visuelle Kontext beeinflusst das fMRI-Signal im LOC. Dieser Kontexteffekt liess sich
durch Modulation der Figur-Grund-Trennung beeinflussen. Hierzu führten wir zusätzliche räumliche Information, Bewegungsinformation beziehungsweise Priming der Figur ein. Die beobachteten Ergebnisse führen zu dem Schluss, dass der LOC Informationen über den Kontext einer Figur erhält,
dieser Kontexteffekt jedoch durch Figur-Grund-Segmentierungsprozesse moduliert wird.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-158Kontexteffekte auf die Formverarbeitung in höheren visuellen Arealen des Menschen1501715422JastorffKG20037JJastorffZKourtziMAGieseTübingen, Germany2003-02-001526. Tübinger Wahrnehmungskonferenz (TWK 2003)It has been shown, that humans are able to learn to discriminate between dierent styles
of natural movements (e.g., gaits or sports movements). However, it remains unknown
whether this learning is based on innate templates for biological movement patterns, or
if humans can learn representations of new arbitrary complex movements. We address
this question by investigating whether subjects can learn articial biological movement
stimuli. Methods: We generated biological motion stimuli by linear combination of
prototypical trajectories. Spatio-temporal linear combinations were computed using
special algorithm, spatio-temporal morphable model (Giese & Poggio, 2000, International
Journal of Computer Vision, 59-73). The following two classes of stimuli were
generated: (A) stimuli derived by linear combination of dissimilar natural movements
(e.g., walking, kicking and dancing). (B) Stimuli generated by animation of an articial
skeleton model that is highly dissimilar from naturally occurring body structures. The
joint angle trajectories of the skeleton were given by linear combinations of synthetic
trajectories. These trajectories were sinusoidal functions. Their amplitudes and frequencies
were approximately matched with the joint trajectories of human actors during
natural movements. Subjects had to discriminate between pairs of these stimuli that
were dened by linear combinations with slightly dissimilar weights. The trajectories
were presented as normal point light walkers (PLW), and as point light walker with position
jitter (PLWJ). The PLWJ were generated by adding random displacements of the
dots along the skeleton of the walker for in each frame. Each subject took part in two
training and three test blocks. Feedback was provided only during training. Results:
Subjects trained with stimuli derived from natural movements (group A) learned the
discrimination between novel patterns very quickly (about 8 repetitions). For rotation
of the test stimuli against the training stimuli we found transfer only for the normal
PLW, but not for the PLWJ stimuli. Subjects were able to learn the completely arti-
cial stimuli (group B) presented as PLWJ equally fast as the stimuli from group A.
Conclusions: (1) New templates for movement recognition can be learned very quickly.
(2) Learning aects at least two dierent levels of representation (local and holistic).
(3) The learned holistic representations seem to be view-dependent. (4) There seems
to be no signicant dierence in the learning process between stimuli derived from
articial and natural movements.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-152Learning of Articial Biological Motion: A Comparison Between Natural and Synthetic Trajectories15017154211501715422HuberleDLBK20037EHuberleADeubeliusWLutzenbergerHHBülthoffZKourtziTübingen, Germany2003-02-001516. Tübinger Wahrnehmungskonferenz (TWK 2003)Recent studies have shown that global information about shapes is processed in both
early ventral (i.e. V1, V2, Vp, V4) and higher occipitotemporal visual areas (i.e. Lateral
Occipital Complex-LOC). However, the temporal properties of shape processing
across visual areas in the human brain are largely unknown. We addressed this question
in a combined fMRI and MEG study that made use of the high spatial resolution
of fMRI and the temporal resolution of MEG. We used an event-related adaptation
paradigm in which lower neural responses are observed for two identical than two different
consecutively-presented stimuli. The stimuli were closed contours that consisted
of collinear Gabor elements. We manipulated the interstimulus interval (ISI: 100 vs.
400 msec) between the two consecutively-presented stimuli in each trial. To ensure
comparability between fMRI and MEG results, subjects participated in both parts of
the study. The fMRI results for 11 subjects showed adaptation for both the short and
the long ISI in the LOC but only for the short ISI in early visual areas. The MEG data
showed similar patterns of response amplitude to the fMRI data and dierences in latencies
for the dierent ISIs across visual areas ranging between 70 and 160 ms. These
ndings suggest sustained shape processing in higher visual areas compared to more
transient visual analysis in early visual areas. Further studies test the analysis of local
vs. global shape features across areas with dierent temporal processing properties.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-151Temporal Properties of Shape Processing Across Visual Areas: a
Combined fMRI and MEG Study1501715422150171542119587CFAltmannZKourtziMErbWGroddHHBülthoffOrlando, FL, USA2002-11-0032nd Annual Meeting of the Society for Neuroscience (Neuroscience 2002)The detection of visual targets against their background is critical for shape perception. The human lateral occipital complex (LOC) has been implicated in the processing of shapes. We tested whether the LOC processes information about the context (background) of shapes. We addressed this question by using event-related fMRI adaptation in which lower neural responses are observed for two identical than for two different consecutively presented stimuli. The stimuli consisted of displays with a closed target contour of collinear Gabor elements embedded into a background of randomly oriented Gabors. There were four different conditions: (i) identical image, where the two stimuli in a trial were the same; (ii) different shape, where the target shape was different; (iii) different context, where the target shape was the same but the background was different; (iv) completely different, where both the target shape and the background were different. We observed adaptation in the LOC when the target shapes were presented in the same background, but no adaptation when they were presented in different backgrounds. These findings suggest that neural populations in the LOC process information about the context of visual shapes.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published0Contextual Grouping effects on Shape Processing in the human visual cortex1501715422150171542127307GAKelirisSMSmirnakisZKourtziASToliasNKLogothetisOrlando, FL, USA2002-11-0032nd Annual Meeting of the Society for Neuroscience (Neuroscience 2002)Perceptual filling-in refers to the fading of stabilized retinal patterns and their replacement by non-stabilized surrounding patterns. We used functional magnetic resonance imaging (fMRI) to investigate neuronal correlates of perceptual filling-in induced by a dynamic random dot pattern. The stimulus consisted of a moving random dot pattern on dark background surrounding a region devoid of dots (artificial scotoma). The subjects fixated at an eccentrically located spot, and they reported the time of onset of filling-in by button press. We controlled for attention by dimming the fixation spot at random points in time, which the subjects reported via a separate button press. Catch trials in which the stimulus physically filled the artificial scotoma were interspersed with filling-in trials to gauge the subjects performance. General linear model techniques with appropriate predictors were used to define areas of interest for analysis. Filling-in trials for each subject were divided in two groups of 30 trial
s each, based on whether filling in occurred earlier (&amp;lt;8 s) or later (8-24 s) in a trial. The stimulus was identical for all trials. Preliminary results suggest that the fMRI signal from area V1 rises initially in both groups but then dips and remains low for the group with early filling-in. This suggests that filling-in is associated with a relative suppression of cortical activity. Other interpretations will be discussed.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published0FMRI Correlates of Perceptual Filling-in in a Moving Random Dot Paradigm150171542115617ZKourtziASToliasMAugathNKLogothetisOrlando, FL, USA2002-11-0032nd Annual Meeting of the Society for Neuroscience (Neuroscience 2002)The aim of the study is to understand the perception of global shapes from local image features. Specifically, we tested the role of various visual areas that are characterized by neural populations with different receptive
field size in the integration of local features into global shapes at different spatial scales. To this end, we used fMRI in the anesthetized monkey and employed an adaptation paradigm. The paradigm entails prolonged presentation of a stimulus, resulting in decreased fMRI response, after which a change in a stimulus dimension elicits rebound of activity. The magnitude of the rebound correlates with the selectivity of an area to the changed dimension. The adapting stimulus was a rectangular area filled with randomly oriented line segments, followed by one of three test stimuli: a pattern identical to the adapting stimulus; a pattern where 1/3 of the line segments changed orientation randomly; a pattern in which change of line segment orientation resulted in a colinear shape. Spatial scale was manipulated by changing the size and the distance between the line segments. Differential responses to colinear shapes and random patterns indicated areas (V1,V2/V3) with neural populations that are selective for the global configuration of shapes, rather than local features. Rebound was observed in peripheral and central V1 for collinear shapes at large and small scales respectively. These findings suggest, that in the processing of global shapes from local features different visual areas are involved at different spatial scales.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published0fMRI responses to visual shapes at different spatial scales150171542113227CFAltmannZKourtziWGroddHHBülthoffSarasota, FL, USA2002-11-00491Second Annual Meeting of the Vision Sciences Society (VSS 2002)The perception of visual shapes entails that local features are integrated into global visual forms. The human lateral occipital complex (LOC) has been implicated in shape processing. We tested whether the LOC is involved in the integration of local features into visual shapes using event-related fMRI at a 1.5T scanner. The stimuli consisted of a. random patterns; that is, displays of randomly oriented and positioned gabor elements and b. target shapes; that is, displays with a closed contour of collinear gabor elements embedded into a background of randomly oriented gabors. We observed stronger fMRI responses in the LOC for target shapes than for random patterns, suggesting that the LOC represents visual shapes and not simple image features. We further manipulated the detectability of the target shapes by varying the alignment of the gabor elements. Misalignment of the local gabors resulted in decreased target detection performance and fMRI responses in the LOC. In contrast, we observed improved detection performance and increased responses in the LOC when the segmentation of the target shapes from their background was facilitated by additional visual cues, such as motion or disparity. Our findings suggest that neural populations in the LOC are involved in the integration of local image features and the representation of visual shapes.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-491Integration of local features into visual shapes in the human visual cortex1501715422GieseJK20027MAGieseJJastorffZKourtziOrlando, FL, USA2002-11-0032nd Annual Meeting of the Society for Neuroscience (Neuroscience 2002)Natural biological movements can be easily recognized from point light stimuli. Learning might play an important role in the representation of such patterns as suggested by recent experiments that demonstrate that subjects can learn to discriminate style differences between natural movements. Such experiments do not answer the question whether such discrimination exploits representations of natural movement patterns that are already present, or if subjects are able to learn quickly novel representations for arbitrary complex movement patterns. To test this question we created artificial biological motion stimuli by motion morphing through linear combination of prototypical trajectories from dissimilar natural movements in space-time. These stimuli have similar low-level motion properties as natural patterns, but do not correspond to movements that can be executed by natural organisms. 14 subjects were trained with seven such artificial patterns in two training blocks, and tested in a discrimination experiment within a pair comparison paradigm. We found a robust learning effect with significant improvement of the performance after 10 to 20 presentations of the training stimuli. Testing subjects with (2D) rotated stimuli we found only weak view dependence of the discrimination performance. This result is potentially based on subjects using primarily local cues for the discrimination. Current experiments investigate the influence of global vs. local strategies on the view-dependence.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published0Learning of artificial biological motion patterns15017154221501715421KourtziBEG20027ZKourtziHHBülthoffMErbWGroddSarasota, FL, USA2002-11-00122Second Annual Meeting of the Vision Sciences Society (VSS 2002)Perception of object motion requires that the visual system integrates shape and motion information about objects. However, recent fMRI studies have implicated separate human brain regions in the analysis of motion (MT/MST) and shape (lateral occipital complex-LOC). We tested whether MT/MST is involved in the analysis of both object shape and motion using fMRI. We observed higher responses to intact than scrambled images of objects in the LOC and MT/MST, especially in a ventral subregion of MT/MST, suggesting that regions involved mainly in the processing of visual motion are also engaged in the analysis of object shape. These object selective responses in MT/MST were observed for moving objects and static 3D objects defined by disparity or shading but not for 2D silhouettes of objects. In contrast, these object selective responses were observed in the LOC for all of these object types. Further studies tested responses to shapes defined by different cues (i.e. disparity, motion or shading) by using event-related fMRI adaptation. Lower responses for the same shape defined by different cues than two different consecutively-presented stimuli implicate neural representations of shapes independent of the cues that define their contours. Our findings suggest differential processing of visual shape in the LOC and MT/MST.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-122Shape processing in the human motion area MT/MST150171542219597CFAltmannZKourtziWGroddHHBülthoffGlasgow, UK2002-08-009125th European Conference on Visual PerceptionThe detection of visual targets against their background is critical for shape perception. The human lateral occipital complex (LOC) has been implicated in the processing of shapes. We tested whether the LOC processes information about the context (background) of shapes. We addressed this question by using event-related fMRI adaptation in which lower neural responses are observed for two identical than for two different consecutively presented stimuli. The stimuli consisted of displays with a closed target contour of collinear Gabor elements embedded into a background of randomly oriented Gabors. There were four different conditions: (i) identical image, where the two stimuli in a trial were the same; (ii) different shape, where the target shape was different; (iii) different context, where the target shape was the same but the background was different; (iv) completely different, where both the target shape and the background were different. We observed adaptation in the LOC when the target shapes were presented in the same background, but no adaptation when they were presented in different backgrounds. These findings suggest that neural populations in the LOC process information about the context of visual shapes.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-91Contextual effects on shape processing in the human visual cortex1501715422GieseJK2002_27MAGieseJJastorffZKourtziGlasgow, UK2002-08-0011711825th European Conference on Visual PerceptionBiological movements can be easily recognised from point-light stimuli. It is still unclear how the visual system accomplishes this recognition. Some properties of biological-motion recognition, eg the inversion effect, suggest that recognition is based on learned templates. This hypothesis predicts that humans should be able to learn arbitrary new movement patterns, even if they do not correspond to movements of a real biological organism. We tested this hypothesis in a very direct way by creating artificial movements through motion morphing. Using a special technique, we computed linear combinations of very dissimilar prototypical movements that were obtained by motion capturing. Such linear combinations specify very similar low-level motion information as that specified by the prototypes, but define movements that cannot be realised by a human. The stimuli were presented as point-light walkers in a discrimination experiment with a pair comparison paradigm. By varying the weights of the linear combination we could gradually vary the spatiotemporal similarity of the stimuli. We found a robust learning effect for the discrimination task, but only if subjects received feedback during training. Also, we found partial transfer between upright and rotated figures. We interpret these results as evidence that learning might play a fundamental role in the recognition of biological motion.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published1Learning to discriminate artificial biological-motion patterns1501715422150171542113277CFAltmannZKourtziWGroddHHBülthoffTübingen, Germany2002-02-00805. Tübinger Wahrnehmungskonferenz (TWK 2002)The perception of visual shapes entails that local image features are integrated into global configurations that represent visual forms. The lateral occipital complex (LOC) in the human brain has been proposed to be primarily involved in the visual analysis of shape. The goal of the present study was to investigate the role of the LOC in figure-ground segmentation and contour integration of simple geometric shapes by using event-related functional magnetic resonance imaging in human subjects. The stimuli consisted of arrays of Gabor elements. Two types of stimuli were used: a) random patterns that consisted of randomly oriented and aligned Gabor elements and b) contours that consisted of a set of Gabor elements that were aligned to a closed contour and embedded in a background of randomly oriented Gabors. We independently localized the LOC in each subject and tested fMRI responses in this region of interest. Our first experiment showed stronger activation in the LOC for contours than for random patterns. Moreover, we found stronger activation in the LOC when the detection of contours was facilitated by additional visual cues, namely motion or disparity. In a second set of experiments, we degraded the contours and found decreased activation in the LOC when the contours were difficult to detect from their background. Our findings suggest that neural populations in the LOC are involved in the integration of local image features and the visual perception of shapes.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-80Integration of local features into visual shapes in the human visual cortex1501715422KourtziK20017ZKourtziNKanwisherSarasota, FL, USA2001-12-00205First Annual Meeting of the Vision Sciences Society (VSS 2001)The human lateral occipital complex (LOC) has been implicated in object recognition, but it is unknown whether this region represents low-level contours or more abstract descriptions of object shape. We tested this question using event-related fMRI adaptation in which lower neural responses are observed for two identical than two different consecutively-presented stimuli (Kourtzi & Kanwisher, 2000). Adaptation across a change between the two stimuli implicates a common neural representation invariant to that change. We found adaptation in the LOC when perceived shape was identical but contours differed because occluding bars occurred in front of the shape in one stimulus and behind the shape in the other. However, in a second experiment we found no adaptation when contours were identical but perceived shapes differed because of a figure-ground reversal. Further studies showed adaptation across small rotations of objects either in the frontal plane or in depth, but not across mirror-image reversals or changes in the 3D configuration of objects. These results indicate that the LOC represents not simple image features but higher-level shape information.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-205Processing of perceived shape vs. contours in the human lateral occipital complex15017154221501715421CulhamDWKGMG20017JCCulhamJFXDeSouzaSWoodwardZKourtziJSGatiRSMenonMAGoodaleSarasota, FL, USA2001-12-00194First Annual Meeting of the Vision Sciences Society (VSS 2001)Purpose: Visual processing is dissociated between a dorsal (occipitoparietal) stream for action and a ventral (occipitotemporal) stream for perceptual recognition. Visually guided grasping requires processing of object shape, but for the purposes of action rather than perceptual recognition. By comparison, visually-guided reaching requires transporting the hand to the target location but not shape processing. We used functional magnetic resonance imaging (fMRI; 4 Tesla) to determine whether grasping (compared to reaching) produced activation in dorsal areas, ventral areas, or both. Methods: Rectangular objects of varying length and orientation were mounted on a rotating drum that subjects viewed directly without mirrors. On each trial, one of the objects was illuminated and the subject grasped the rectangle along the long axis using a precision grip (with the finger and thumb). In a control condition, subjects reached and touched, but did not grasp, the target object. Event-related single trials took advantage of the hemodynamic delay to dissociate true grasping-related activation from potential motion artifacts. Results: In each of six subjects, grasping produced greater activation than reaching in the anterior intraparietal (AIP) cortex. Negligible grasp-specific activation was observed in ventral stream object areas. Conclusions: These results suggest that the processing of shape required to form a grasp involves dorsal but not ventral stream regions. The dorsal stream area that was activated is a likely human homologue of monkey AIP, an area containing neurons that code object shape and fire during grasping.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-194Visually-guided grasping produces fMRI activation in dorsal but not ventral stream brain areas1501715422150171542110637ZKourtziASToliasBAPrauseMAugathTTrinathNKLogothetisSan Diego, CA, USA2001-11-0031st Annual Meeting of the Society for Neuroscience (Neuroscience 2001)The aim of the study is to understand how local image features are integrated into configurations that may represent visual forms. We used fMRI in the anesthetized monkey and employed an adaptation paradigm (sufficiently prolonged presentation of a stimulus resulting in decreased fMRI responses over time) to test the role of various visual areas into such an integration process. The stimuli consisted of target-shapes embedded in a background of randomly oriented lines. The target-shapes were defined by collinearly arranged lines of the same height and width as the background lines. Following the presentation of an adapting stimulus, three conditions were tested:(A)presentation of a pattern identical to the adapting stimulus, (B) presentation of the same target-shape as the adapting stimulus but embedded in a different background (i.e. the background lines were rotated 90 deg), and (C) presentation of a different target-shape (orientation-changes of target rather than background lines). The selection of these conditions was motivated by the hypothesis that increased responses in the test phase for a new pattern are likely to indicate areas with neural populations that are selective for the global configuration of shapes, rather than local features. Initial experiments show that the time course of the fMRI signal varies in different visual areas. Not surprisingly, early visual areas failed to show shape selective adaptation, suggesting that the neural populations in these areas primarily encode local features. Differences in the time course of adaptation in higher visual areas are currently studied using a variety of visual patterns.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published0fMRI adaptation for visual forms in the monkey brain1501715421BulthoffKEG20017HHBülthoffZKourtziMErbWGroddSan Diego, CA, USA2001-11-0031st Annual Meeting of the Society for Neuroscience (Neuroscience 2001)Recent human fMRI studies have implicated separate cortical areas in the analysis of visual motion (i.e. MT/MST) and the processing of object shape (i.e. lateral occipital complex-LOC). However, the perception of object motion requires the visual system to integrate information about the shape and the motion of objects. Is MT/MST involved in the analysis of both object shape and visual motion? We tested this question by collecting functional MRI images with echo-planar head coil imaging at 1.5T while subjects viewed visual stimuli of various kinds. First we localized MT/MST and the LOC individually in each subject and then we tested for fMRI responses in these regions when the observers were presented with intact images of objects and scrambled versions of the same objects that have no clear shape structure. Higher responses to intact than scrambled images of objects were observed in both MT/MST and the LOC. These object selective responses in MT/MST were observed for moving objects and static 3D objects defined by binocular (i.e. disparity) or monocular (i.e. shading) depth cues but not for 2D silhouettes of objects. In contrast, the LOC showed shape selective responses to all of these types of objects. These results implicate MT/MST in shape processing and perhaps in integrating information about the shape and motion of objects. Moreover, the strong response to 2D shapes in the LOC but not in MT/MST suggest that the LOC may be involved in the recognition of both 2D and 3D objects, whereas MT/MST may be involved in the visual guidance of object-directed actions.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published0Object selective processing in the human motion area MT/MST1501715422JastorffKG2005_210JJastorffZKourtziMAGieseJastorffGK200410JJastorffMAGieseZKourtziJastorffGK2004_310JJastorffMAGieseZKourtziKourtziBS200310ZKourtziLBettsPSarkheil239510CFAltmannZKourtziKourtzi200310ZKourtziTjanLKGB200210BSTjanVLestouZKourtziWGroddHHBülthoffKourtzi200110ZKourtzi